In Old English, at least according to the online Old English Translator, there were two words, the adjective blæc, which meant black and the adjective blac, which meant pale, shining, white, along with the related verb blæcan, which meant to whiten, bleach.
In Old English, "æ" and "a" were different letters, the first pronounced like the vowel in cat and the second, the vowel in father. These two vowels merged in Middle English, and presumably led to two homophones which meant, respectively, black and white. This certainly seems to be too confusing for both words to exist simultaneously, but maybe different dialects used one or the other, which would cause the confusion as to what blaec meant in Middle English.
The first led to the Modern English word black and the second to the Modern English words bleak and bleach.
How did these two words, pronounced nearly the same, end up in Old English? They seem to have both descended from the Indo-European stem bʰleg- meaning to burn, shine. (There is some controversy about this, but it seems quite plausible.) According to the OED, the adjective blæc is
cognate with Middle Dutch blac ink, Old Saxon blac ink (Middle Low German blak ink, black dye, black colour), Old High German blah- [...] ink
and the adjective blac is cognate with
Old Norse bleikr shining, white.
There is also
Middle Dutch blaken (Dutch blaken) to flame, to burn.
Putting these facts together, one can construct plausible etymologies:
bhleg-, meaning shine, burn → burn → burnt → ink (made with burnt carbon) → the color of ink = black.
bhleg-, meaning shine, burn → shining, white, pale.
So the black meaning seems to have come into English by way of the Saxons, and the white meaning by way of the Vikings, but both quite plausibly originated in the proto-Indo-European stem bʰleg-.
And in Middle English, it seems that blaec, blak, blake (Middle English spelling is notoriously inconsistent) could mean either black or white (although possibly in different dialects).
And blanc, blanche (French) indeed came from the same proto-European stem. So the news article seems completely correct.