GR 5.10 specifically prohibits mercy killing a player to help them avoid a roleplay situation. It also prohibits finishing/executing a downed player while an active incident is still ongoing. A player may only be finished once all active hostilities have ceased and the roleplay situation has concluded.
Based on the POV, this does not appear to be mercy killing, as there is no indication that the player was killed to help them avoid the ongoing roleplay situation. Therefore, GR 5.10 does not apply in this case.