I think it might be more accurate to describe the quoted language as a descriptive summary than as a rule, since it can be difficult to predict when a collective noun will be interpreted as taking a plural verb instead of a singular one, unless you're accustomed to the prevailing practice in your area.
When I moved from Texas to Alberta as a teenager I had a lot of trouble anticipating which nouns Albertans would interpret differently from the way Texans did. For example, in U.S. English, a sportscaster would say "Houston has the football at its own 49 yard line"; but in Canadian English, a sportscaster would say, "Calgary have the football at their own 53 yard line." On the other hand, both sportscasters would agree on "The Oilers/Stampeders have the football," and (if I remember correctly) on "the team has won three games in a row."
So while it's straightforward enough to observe that some collective nouns that look singular take a plural verb when they are interpreted as emphasizing the component individuals that make up the collective body rather than the that body as a unitary thing, its not so easy to anticipate when such interpretations will occur.
Bryan Garner, Garner's Modern American Usage (2003), which argues for consistency within a single piece of writing, acknowledges the slipperiness of collective nouns:
But switching back and forth between a singular and a plural verb is lamentably common: "Mark Pattinson's Memoirs is not strictly speaking an autobiography .... His Memoirs do not so much tell the story of his life .... Mark's father, as the Memoirs make plain, dominated his son's early years .... The Memoirs describes clearly." V.H/H. Green, Introduction, Mark Pattinson, Memoirs of a Oxford Don 1, 6 (1988). Here the problem seems to arise because the author can't decide on a constant use of the common noun memoirs, which may be used as a plural noun but should not be capitalized, and the proper noun Memoirs, which is the singular title of the book.
Garner also notes that the preference for unitary interpretation of collective nouns is stronger in the United States than in many other former British colonies, and in the UK itself, though it is by no means absolute, as we see in such formulations as "the majority support" and "the faculty oppose."
Ultimately the decisions that people in a country or region make about whether to treat a collective noun as singular or plural appear to be idiosyncratic and fortuitous, rather than determined by logic or applied rule. If so, the only way to determine whether a particular collective noun should take a singular verb or a plural verb is to listen to what other people in the area say and write.