There is nothing more the law hates, than when people wait without any actual good reason. If anything, I would say that would make the person look more suspicious.
Point of the matter is, unless the OP did something, he has nothing to worry about. Being questioned and answering the questions honestly is simply the best thing he could do. If he has nothing to do with what was going on over there, it will be known.
Yes, but if you are suspected of it, they will simply question you. They are not going to detain you or anything, and it should have absolutely no effect on you becoming a fire fighter. Also as I said, waiting may make you more suspicious if something was done with the camera. If you didn't do anything, there is no reason for you to wait.
It's the same reason when someone runs from the cops, they automatically assume the person running is running because they broke the law. They instantly become a suspect because they did something suspicious.