I don't see anything wrong with what is in there. Even if there was a mistake it shouldn't be causing a crash like that?! (I've not actually seen a crash error like that before. It has perked my interest). I take it the 'carvariations.meta' & 'carcols.meta' that reference the vehicle are somewhere else in the game? Again, even if they are not, the game should load, just the AUDI80Q won't spawn.
If you're happy to do so, the best way for me to work on this is if you give me a copy of your AUDI80Q 'dlc.rpf'. That way I know it's identical to what you have/if it works in my game it will be diagnostically informative etc . If you're cool with that upload it to mega.nz or something & share the link with me. You can private chat me if you don't want the link to be public
Check my profile on here if you have any doubts, I'm only interested in helping people