That'd never fly. And it shouldn't.
First and foremost, there are very specific laws relating to citizen's arrest....when they can be made, how they can be made, etc. In many states, had the car window not been broken (in other words, the car was unlocked), it would have been a misdemeanor. Many states only allow citizen's arrests in the case of a felony. (Which this was, so it's immaterial.)
I don't know about this lawsuit; frankly, the details are sketchy. In fact, I don't even see that the state of Florida has a statute permitting citizen's arrest. They may permit them in all felony cases. They may permit them if one is apprehended inside of a store, for example. Orrrr, they may not permit them at all.
In any case, in a citizen's arrest, the "citizen" does NOT enjoy the same protections a law enforcement officer does in effecting it. Frankly, if I were on the jury in this case, I would really raise my eyebrows that three citizens were involved in detaining this (apparently unarmed) guy -- and that one of them pointed a gun at him. Threat of deadly force over a bicycle is waaay over the top. These citizens are no doubt going to be punished whether they are found to be liable or not. Defending oneself against such a lawsuit, even if it's dismissed quickly, costs a small fortune. You can be sure that the judge will give this claimant lots of latitude because he's pro se.
I think they're in trouble myself.