Somehow, the knowledge Peter was teleporting hadn't been all that comforting, and leave it to Nathan to be the one not comforted by travel that left people virtually unexposed because it could happen so quickly. Right now, any exposure to danger where Peter was concerned understandably didn't sit well with him. Add in the details of the future Hiro had just revealed and he was finding it hard to keep entirely calm and relaxed about an arrival from Peter's timeline.
Peter wasn't in the lobby when he he got there, but Nathan knew that could change rather quickly, so he folded his arms over his chest. Gaze -- or, more accurately, glare -- sweeping the lobby, he waited.