Yeah, as I alluded about 8 posts up, that's possible (not necessarily certain). He didn't come right out and mention it - but then again, he wasn't exactly best buddies with the person he was talking to, so their conversation would have been awkward no matter what. Plus, he might have been in some shock after the alien confrontation, and was just then in his mind going over the water weakness and putting it together with the signs' locations (which would be much more likely, imho, than noticing where the signs are and working backwards to deduce they dislike water) and just said right then as he thought of it.