I don't think he was childish, no. I watched the interview, it was really bad how the other 2 were trying to steer the focus away from the homophobic aspect and generalise it as a terrorist attack, when it was both.
I understand his frustration. He was being shut down on all sides, he even tried to stop them saying the man was a lunatic rather than a homophobe (as though you'd have to be mad to be homophobic, which is definitely not the case) and was told by the woman that she could choose her own words, thanks. Well yes you can, but if someone suggests that they're inappropriate for a reasonably good reason, then it would be polite to listen! not continue to talk over that person.
Yes Owen also talked over them, because he couldn't believe what they were trying to do.
Anyway, no he wasn't childish, he was upset and incredibly frustrated with the way it was all going.