In all honesty Trevor's response was more out of reflex than anything else, since as he knew so little of Suuichi he couldn't rightly say whether or not meeting him was a pleasure just yet. He was wary of almost everyone he met even when he wasn't dealing with giant killer insects; it wasn't anything personal. Trevor just liked to be bluntly honest in his exchanges with others, except Sypha. He sometimes attempted to shield her from just how bleak and scarring his outlook on life was.
"The only place I have to be is somewhere safer than out in the open." Assuming any conversations this Suuichi might want to have were going to be short in nature or not expecting much in the way of verbosity from Trevor, he didn't mind continuing to chat with the somewhat odd flower whip wielder.