Flyover person is a derogatory term meaning people coming from the rural areas and small towns in non-coastal parts of the US. These are places where the speaker feels that nothing interesting ever happens and whose inhabitants get put down for supposedly having little education and for being backward and boring by those flying over them.
It is basically every area you “fly over” on a plane to get to locations on the East or West Coasts where the speaker feels that everything that’s important or interesting happens and where anyone who’s sophisticated lives.
The term flyover does not need to be derogatory, but often is.
There's a book called Flyover Nation: You Can't Run a Country You’ve Never Been To by Dana Loesch where the author glorifies flyovers and compares them to coastals. Read the brief summary here.