Let me jump in with one minor point for you all to consider. I will preface this by saying that I agree with the OP on what he did and with Charles' summary of the law. I would have handled it almost exactly like the officer involved did, though I might also have arrested the biker.
But Alvins is also technically correct. And he did say technically. It is aggravated assault and/or deadly conduct to point a pistol at someone. This is illegal and you can be arrested for it. All of the justifications under chapter 9 are "defenses" to the charge, which does not affect the legality of an arrest. It means you should win the court case but you could be arrested. With any reasonable officer, a justified use of your firearm will mean you will not be arrested, but we should all remember that the possibility does still exist.
As a side note, the OP was also lucky not to get an accident on his driving record. Even with all of the rest going on, when the bike rear-ended the car, it was still a crash that belongs on a report. The report should have shown the OP not at fault, but do you trust the insurance companies to agree?