To be fair, antifags are so goddamn inept I would be more surprised if the shit DID detonate. Not to mention that sometimes even perfectly made bombs can fail. I remember years ago when the police, I think it was in New York, ended up being tipped off by an Egyptian man about his Arab roommates building bombs. They stormed the place in full tac gear with body bunker shield and all and managed to quickly aprehend all but one of the terrorists who managed to grab a bomb and hit the detonation switch just before being shot. The bomb failed. But when the forensic team built a series of exact replicas of the bombs each detonated without fail.
Either way, I'd probably clear the area and detonate the car just to be safe.