"Dont most aerodynamists come from the aviation industry first? i.e. airplane design engineers"
I think in F1, yes, but in the rest of the auto industry it seems to be the case that mechanical engineers often get moved or choose to move into aero roles and then pick a lot of it up as they go along.
I did Physics originally at Uni then realised my fate would probably in either computer programming or accountacy so did a Masters' in aero before trying unsuccessfully to get into F1. I then spent 8 years doing aero consultancy on road & race cars of all kinds plus trucks, buildings and all sorts of random things (like bird tables!).
As of next week though, i will finally have achieved my goal since i start as an Aerodynamicist at Williams F1. It's like the American Dream, only British.