The police "smelled pot". That's probable cause. It's possible that one of them had previously smoked some in the car, maybe some time ago (let's be honest - anyone who has a pipe in their car has probably used it, but that's not the kind of thing which will stand up in a court of law without also finding a stash).

But seizing a car because it's got a pipe in it is insane. Even if they had a small quantity of pot, that's crazy - a small stash for personal use doesn't make someone a dealer.