Trap Kill trophy buggy?

[theninja223]

When I did the Bomb Kill, I did it in trios and I've killed a red bar enemy (he was "downed"). But now, after a long time, I'm trying to do the trap kill in trios but it doesn't unlock. I think I did it three times now.

Some people in here said that it doesn't work on trios and some other people said it did but now I'm confused. What do you guys think? Do you think they changed the trophy to only work in solo?

Here it is the video of my last attempt. Did I do something wrong or is this the way of making the trophy pop?