Wait, yeah, this doesn't sound right at all. Carroll provides exceptions for cars where there is probable cause. I too would be surprised that 'unlocked door' constitutes probable cause.

Though, here the police are explicitly giving the items back (if the backpack they take doesn't have weed, I guess). Civil forfeiture, as a practice, is legal but really shitty (if the police think you made money from a drug ring, you're never touching that money again, even if you're acquitted).