Amex's preference for PIF is something that is accepted "in general," not a universal truth. For instance, Citi & Barclay prefer people carrying balances, but this is true "in general," and not in every case.
In other words, generalities are neither proven nor disproven, unlike a hypothesis. For example, in general, males are physically stronger, taller and run faster than females; just because the 100 Meter Woman's Gold medalist or Ms. Olympia is faster and stronger than most men *does not* invalidate, that, "in general," males are taller, stronger and run faster.
If I assert a hypothesis, such as, Amex CLIs cardmembers who carry a balance more than 13 months. In this case, your wife carrying a balance greater than 13 months without suffering a CLI would refute the aforementioned hypothesis (which must be true 100% of the time, unlike generalities). This, would be a "myth" or "truth" buster, refuting and disproving a working hypothesis.
So, in general, many find Amex's spendcentric model to favor PIF cardmembers, while Citi/Barclay's interest revenue model will tend to favor those who carry balances. An exception in these issuer's general practices neither refutes nor disproves the general characteristics of each issuer's chosen business model.
*Edited* PS - Amex is the *ONLY* CC I know of based primarily on a spendcentric (however, with the ED cards, they seem to be diversifying towards some interest based revenue) business model, though Chase comes close.
