OK, to wade in without full information in the traditional STW way… ;-)
It could be interpreted that OP was going to sleep off a couple of drinks in their car in a carpark.
Carpark attendant tells OP he can’t sleep in his car.
Discussion follows.
OP leaves car and sets off walking (complete with car keys).
Carpark attendant rings police with description, police pick up OP, complete with car keys, and asks him to blow into this please sir.
OP (in the eyes of the law) is drunk in charge, does seem more that somewhat harsh to me though.