Back up on the roof Matthew says,
The portal's.... and catches himself before he says "gone". Hmm. Don't want to give away any information in front of the prisoner.

The portal's certainly very powerful magic. So is whatever torched these men. Vlax, Ioth, Matthias can you help me a sec? If you're not busy? I want to grab some plants from that forest through the portal to help identify exactly where it is on the other side.

If they come downstairs he says, "Sorry for that ruse. I didn't want to tell the prisoner the portal has gone already. You guys must have got back out not a moment too soon."