I'm thinking it's one of the Cerberus Vents (noted as "CV" on the some of the stations on the blast door map). These Vents were supposed to act as an escape route from the monster.

I would surmise that Ben attracted the monster in some way and then led it towards the armed freighties. I don't think he has control of the monster because he does forewarn everybody to stay away from the freighties when they run into the tree line. If he had complete control of the monster, he would have simply commanded it to only attack the freighties.

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Abaddon