Here is footage of an Israeli boat before the landings.
Who would you say is attacking who?
How much incoming fire is there?

First of all, there is no way to know that this footage was taken before the Israelis boarded. This video doesn't show any of that. You are taking the Israeli government's word that it happened that way with no evidence to back it up. Secondly, the stun grenade is being thrown back to the Israeli boat. The only reason anyone on the Mavi Marmara had any stun grenades at all is because the Isralis fired them at the Mavi Marmara in the first place. So that answers your question of who is attacking whom.