Harry is the viewpoint character, and he thinks everyone is an idiot except him and Quirrell. He is in error. He has been consistently in error about this since ... forever. It's probably a character flaw that he shares with Voldemort, although Harry has a somewhat less murderous form of it.

For instance, Harry believes that the wizarding economy should be trivially exploitable via exchange with the Muggle precious-metals market. He believes this because even though he knows about half-bloods (i.e. witches and wizards who have a Muggle parent), he thinks that he is special and that nobody else ever would have thought of that.

Similarly, he believes that he is the first to come up with the idea of combining magic and Muggle science. He isn't that, either. He doesn't realize this even after he is given the (ostensible) diary of Roger Bacon.

And here's the thing ... he doesn't update about these errors. He's not particularly curious about them. "Hey, wait, there are Muggleborns; what's the chance any of them has ever had a relative in Muggle banking, finance, or economics?" "Oh, Roger Bacon was a wizard? I had better learn me some Latin so I can find out what the history of magic/science interaction has been."