To be honest, in the first instance, I applaud the pax for standing up and saying something. Afterall, you can say the pax may be amateurs, but the flight attendants are just as clueless. In fact, most of them don't even look out the window on departure, they just chat amongst themselves.
So if someone did see something, better to be safe than sorry, I reckon. At least that way the passengers can be calmed down, and you yourself aren't left wondering.
But then, the crew probably had a duty to explain to the pax why the aircraft was venting fuel. The next couple of attempts, IMO if that was the problem, probably didn't need to happen. However, it could have been the ground engineer's failure to disclose the actual problem (which could be highly likely), or perhaps just pax not understanding proper English.
Pax overreact, that's the general consensus. So what? They pay (well, in this case, not an overly generous amount) to travel from point A to point B, we're paid to make sure they get from point A to point B. If they feel unsure, you either explain exactly what happened so that they understand, or you offload them. That's also our job.