The key which you can't actually see, and don't actually know is there, jingled a bit. You'll have to throw something heavier against the door if you want to knock it loose.
Hey check it out. Every week we'll be revealing some new troll characters from Hiveswap until Act 2 is out. Follow the Troll Call here, and meet the first two here. Expect a few more surprises like this to drop in coming weeks.