There’s been a lot of debate about that and I’ve never seen a definitive answer. There are some identifier codes in Bluetooth which may be used and then there’s the obvious like something called ‘Sync’ might well be a Ford car. There’s some speculation (from people who called random bluetooth devices common car bluetooth names) that there’s an additional criteria that the location services has to detect movement too (though it seems to me that’s not a perfect measure either, for obvious reasons). My personal feeling is that they probably use all of these and a bunch of heuristics but, hell, who knows
Hope the changes you made work out for you. The “Dude, where’s my car” feature, along with the “X minutes to Home/Work/Wherever you normally go at this time on this day” features are genuinely useful imo.