I, too, would perceive it as disrespectful if a friend fiddled with all the not-necessary-to-drive-safely-and-comfortably trinkets in my car - but someone else might not think of it as such, or might not mind at all. Maybe your friend simply did what they'd do in their own car - adjust mirrors, steering wheel, temperature to their own needs, then find their favourite radio station, etc., without realizing that they'd overstep your boundaries in doing so...
As for behaviours that make me nervous and/or annoyed - I can't stand it when people show up unannounced; even less when it's relatives who let themselves in with their (supposedly) for emergencies only key.