Wending Grace

Hello, I am new to the community but I have a question.

Story: Me and my boyfriend were playing night reign together, and we both managed to get a wending grace. We were pretty happy because we were doing the final boss and knew it'd be hard without it. Either way, we get to the final boss and I get down, of course, and my boyfriend comes to get me back up, and he gets downed too, triggering my wending grace. Once I get up, I dodge an attack from the boss and start shooting my boyfriend to get him back up, but then all of the sudden the game auto uses his wending grace, and we end up losing because of it. Is this a bug, or am I just dumb?

Question: Why did the game auto use my boyfriend's wending grace when I was and actively shooting him?

Ps, please be nice I am sorta new to the game. 😔