So you're claiming he was a T as he activated the T trap in the nether?

Did you see him walking through the T room?

If not that your most likely killing on sus. Just because a trap is activated doesn't mean it could only be the person in the nether.

Please provide video proof where you and he were the only one in the nether and you did NOT see him enter the nether through the portal and he wasn't AFK in there.