Va Tech has a national brand in football, and a powerful regional fanbase.
The vast majority of fans for any college team are non-alums. And because Va Tech has been the "good" team in VA for the better part of two decades, of course their fanbase throughout Virginia is quite large. So, to answer your question, I believe the majority of VT fans are non-alums, sure.
Also, with a statewide fanbase, it helps that (a) CVille is pretty easy to get to, and (b) tickets are available aplenty for games in Scott. Once UVA sells 45k season tickets again, then the single-game tickets won't be so easy to snag at face value. But so long as it's an easy ticket, I don't blame them for wanting to show up. It's a fun game!