That is just you being a noob.
Since he is the attacker, as soon as the previous doors dropped, he was killed. Since the doors are now down, he spawns AHEAD OF YOU in the final room, jumped down, and started planting. Some players even seek death as soon as they see their team has planted a bomb, and then just hold off on pressing the "Release" button until the door drops for a free teleport ahead of you.
Oops, I just gave away my secret strategy.
Explain this one then... VS. Attackers *just* drop first door. Charging down to prevent Attackers from dropping shields, bridge, second door. Start attacking mobs, get report from WZ NPC that attackers have just downloaded the intel, WZ over.