I bet someone saw you. Either that or walked by and maybe they weren't covered completely (people don't think about the straps). It's pretty common in large parking lots. Tint and the inside cover would've probably been very good to have. But hey, can't stop it all.
Loki is commentator for other sites as well as the publications: Who's Booty Is That On My Face Magazine, Fart Life and written the self-help book, What To Say To Comments About Your Crack Whore Mom.