I'm surprised that none of the adventurers, the guildmaster especially, called him out on the dragon bone bluff. When he introduces it in the previous chapter he specifically says "I can make a dragon flame just once with this", and then he has to use the spell he's disguising as "dragon flame" twice to kill enough monsters.
I know it's isekai and to not expect too much, but if it wasn't just for page padding, it felt like the author was having him cast twice so that someone would pick up that he was lying about his power, there. But I guess nothing actually came of it.