Yes, the game is a single player action-adventure. There will be other characters in the game, most notably your fellow astronaut crew mate. He will be a guide as you explore the mysterious places you encounter in Lifeless Moon. However, due to a strange Event, you are separated from your crew mate in time. You may catch a glimpse of him or hear him over comms, but it becomes clear the two of you are living in separate time dimensions. Your crew mate is thus a few minutes ahead of you at all times and can sometimes give you clues to what lies ahead. Like Aelita in Lifeless Planet, your fellow astronaut will provide direction and information about the places... and things... you will encounter.
In regards to other characters, we do not want to spoil the story, but we'll just say "Lifeless" is in part an ironic title (it also speaks to the psychological themes of the story)... Yes the Moon is a place of "magnificent desolation," but who knows what places or characters live beyond the Event?