> - "like he knows everything(in reality he doesn't..." -- You don't really know what he knows.
You can't know that for sure.
If, for example, someone is constantly making claims that are factually incorrect, and they are very confident and arrogant in the way they assert these claims. If they are always (factually incorrectly) telling others they're wrong about topics. If they always have to give their view on a topics, even if it's not necessary. In cases like those, it's pretty fair to say they talk like (the OPs actual phrasing) they know everything when they don't.
> - "He can't understand simple logic" -- I'm sure he can understand "simple" logic.
On the basis of what? Plenty of people can't understand simple logic, just like plenty of people have problems with basic maths.
You can't know that for sure.
If, for example, someone is constantly making claims that are factually incorrect, and they are very confident and arrogant in the way they assert these claims. If they are always (factually incorrectly) telling others they're wrong about topics. If they always have to give their view on a topics, even if it's not necessary. In cases like those, it's pretty fair to say they talk like (the OPs actual phrasing) they know everything when they don't.
> - "He can't understand simple logic" -- I'm sure he can understand "simple" logic.
On the basis of what? Plenty of people can't understand simple logic, just like plenty of people have problems with basic maths.