It doesn’t look jammed - and he may have been mag swapping during lulls in the fight/when he got a chance, as you’re supposed to. Last mag being empty is probably the one that was in the gun when they got in close and he was forced to resort to the grenade.
I was thinking he was able to empty one magazine, got some stoppages got panicked and kept switching and then used the grenade on himself because it was the last thing he could count on.