Such a characterization from California - linguistic land's end - melting pot of southern drawl and northern twang - domain of golden misnomers and mangled metaphors - is instructive, but do not dismay.
For much of the previous century, a pocketbook/pocket book (depending...) was a kind of wallet that could be folded and generally snapped shut - those were the stylish days before Velcro and "plasticization" of all things metal - then deposited - i.e., nested - inside a (true-to-life) purse. Inside were kept frequently used things of value such as coins and bills (hence the connection with money) and personal identification; plus whatever small flat items (charge cards, as they were then called) which were desired not to float around inside the purse (not bag) - different from the 1970s onward, when the catch-all bag, and sifting though it or emptying it on the counter became the money retrieval "method" of choice. The pocket book or, less "misnomery," the book pocket, was a kind of "safe pocket" that could exist apart from any pant, vest, or coat; or even from the purse or pocket where it normally resided. It was as if the word for a close-able wallet had an interior and exterior meaning: inward pocket for retention and retrieval of quick cash; outward appearance of a locking, or at least closable, book.
In those days in which the use of as well as reference to "pocketbook" was fairly universal, people quite often also carried a savings account deposit-withdrawal register, called a passbook, which could fit in a pocketbook. (Are you seeing the picture...of having money, ID, coin and bill, and coin & bill receptacle all in one place at a bank counter...? In the urban days before sprawl and cookie cutter mansions had expanded to the remotest reaches along with utter dependency on automobiles, resort to personal funds was a bank en*counter*, not an ATM and not via plastic.
The term, pocketbook, was so ubiquitous it came to have a broader - that is (and no pun...), either of two broader - or would it be narrower - meanings, mostly associated with the carrying of money in general, be it in a purse or in a pocket (as in, within a man's wallet). So the term came to be used in either instance: a woman's or a man's purse or pocket-borne receptacle, respectively, for carrying money. It also came to be used not only for the concealed "book," but also for the containing purse as well. In short, one's pocket book became synonymous with ones carry-around money itself.
...not surprising, then, that pocketbook could also come to represent, almost euphemistically, the very thing it is purposed to accommodate: money. Clearly, in the introductory question, there is meaning between the lines that, with Teutonic paucity of words, alludes to a Germany so rich from the postwar reemergence of its prewar industrial might, that by comparison with neighboring Euro Community countries, it can be thought of in terms of guiltily subsidizing (and not nationalistically destroying) Europe from an economic wealth building capacity so large as to suggest that the cohesion of Europe depends on only the relatively small proportion of treasure "carried about" (as if) in that nation's cache of loose change: its pocket book. In other words, the allusion to the German pocketbook is a way of saying the country's underlying wealth producing capacity is far greater still.
Interestingly enough (back here in the states), the beginning of the end of "pocketbook" universality happened at about the same time as women's pant's zippers moved from the back to the front - pockets and wallets in; purses and pocketbooks out. Now there's an interesting ethnology. As for etymology, the word's having sprung fully formed into speech by virtue of its appearance alone as a kind of book pocket, it really has none: only the simple fact of its (the item's and, more so, the word's) being in vogue for so long, then falling out of vogue (such that its use would be forgotten in California); then coming somewhat back in vogue as yet another of so many "fresh ideas," from the past, increasingly emerging as novel, "all new," products to sell.
Suffice it to say, also, that using the term, pocketbook, is also a short hand way of talking about yours or another person's money on hand without using the word money. In that sense, it is a kind of etiquette word: are you more at ease if someone inquires about a pocketbook, or about your money. Accordingly, there was similarly a measure of status in the use of or speaking about pocketbooks, as opposed to merely carrying/jangling money loosely, or in a wallet, in the pocket or in the purse. Billfolds were blue collar; pocketbooks white collar.
Californian or not, you can take some comfort in the knowledge that there was a time when your bewilderment about misnomers was shared by all curious-minded persons in the passage into adulthood. By the measure of at least one, children in numbers must have wondered about that mysterious thing their parents called a pocketbook, without ever seeing a book going into or coming out of pocket.