Don't you think that was a bit of a stretch?
I mean, he only knows that in one facility on that moon there's some goo that does terrible things to animals it it touches.
And from that he conclude that this is not their home planet but in fact a weapon research facility.
The fact that the goo is a weapon in and by itself seem a bit of a stretch*, let alone his insight about the nature of that planet.
And again, the frustrating thing is that it really wasn't necessarily, I mean, they have a robot who can fucking read and talk the alien's language.
This is just bad writing.