It's ahead so what? I don't really understand. Maybe he didn't launch the 2of them at the same moment but only one quickly before the other. Like maybe also it's because of the wind direction that one has gone ahead from the other. Who knows?
I think he said "it" only in a general case, but maybe i'm making an error. Saying it was better than saying "them" in this case. So i think when he says "it", he wants to say "this thing". Which thing? "the arrows".
Also i don't think Kishimoto would have made his pic so complicated. It would have been much more easier for him to draw one arrow. The second arrow is not really relevant if we are judging like you. Like i've said the water is under them. If you think it's a reflection, that it's a reflection with what?