I don’t see the problem.
When the game becomes no longer fun for a guy, that’s when we’ve lost them/they’ve checked out.
Moral has to be kept up and I don’t see celebrating a small in game victory as an issue, it wasn’t over the top IMO. He was already laying on the ground, it’s not like he ran over to a predetermined spot, laid down and then did it.
I’m just as frustrated as anyone but I won’t hold a small/reasonable celebration against anyone, even if we’re not winning at the moment.
YMMV