Oh, Zoroark, you can be so funny sometimes.
To be honest, if I was the Bronzong's trainer, I wouldn't think anything of it. Many water types can learn Fire type moves, such as Gyarados, Octillery and Slowbro.
You actually listed pretty much the only Water-types (aside from Slowbro's relatives) that can learn Flamethrower and Fire Blast. XD
@SharKing; don't forget Palkia!
edit: now that I think about it, Castform in rain might count as well.