Using proprement to emphasize an idea is not controversial in French. One of the meanings of proprement in the TLFi is:

I.- C.- − [Dans un sens affaibli, vient renforcer une affirm.] Synon. de absolument, totalement.

“Proprement” is really too posh in French (of France) to be an equivalent of “literally”. The closest term I can think of is “carrément” which we use a lot, though it never became a thing in France (maybe in other French-speaking countries?).

What makes you believe that proprement is misused in this sentence? It means that the patterns are especially fascinating in a way that other things aren’t. In brief, d’une manière qui leur est propre (sorry, this cannot be translated without losing the effect I want to give it). One definition of proprement is:

D’une manière qui est spéciale, spécifique à une personne, à un ensemble de personnes, à une chose.

It’s a perfectly good use of the word.

As said, it’s theoretically right to say to use proprement in the meaning of d’une manière qui leur est propre. The thing is that in practice I’ve never heard anyone using this adverb to emphasize an adjective, not even misused. People tend to misuse littéralement sometimes, although less often than the English with litteraly. If you used proprement in that context, you would sound as if translating litteraly from English to French.

Actually the main reason for it is that the first meaning of propre is clean. Proprement means on a clean way like ‘Mange proprement‘ as a parent would say to his child.
Though in some widespread expressions as ‘Proprement dit’ or ‘À proprement parler’, it doesn’t mean clean at all, but rather properly.