Liam was actually enjoying the strange enforced company. Buffy was a delightful girl, and there was something freeing about a new friend to hash out the whole dream insanity. Mordin approached things as clinically as possible but Liam needed a more emotional perspective as well
He also wanted badly to talk to Rose Tyler again. But that seemed like such a dangerous road.
So the distraction provided by Buffy Summers was well timed indeed. He ordered them both coffee, looking around for Finnick. Hopefully speaking with fellow dreamers, as it were, would afford the young man peace of mind.