This is in fact not a discussion about the semantics of performant.
It's imprecise: What is it even supposed to mean? Because it's a made-up word, who knows for sure? Does it mean "better performing?" If so, why not just say that? It's not that many more keystrokes. Better performing in what way? CPU? Resource utilization? Say so. You've put a lot of thought and effort into writing something, why blow it by using an imprecise pseudo-word? The author is undermining his own credibility, telling us "I don't care enough about the topic to even pick an actual word, let alone summarize, in more detail, what I mean to discuss."
My understanding is that performant is totally legal French, meaning efficient or effective, with usage dating back at least 4 decades. If you're not into stealing random words from other languages, I have to question why you're into English in the first place.