In my humble opinion, it would be considered a “shoel”, and the act to be a “maisah machmas melacha”, that he’s not responsible.
When someone comes to your home you either offer him a seat or he takes one on his own, knowing that that is your desire, that he be seated. You know he’s not taking it home, he’s using it, and returning it.
As long as nothing out of the ordinary occurs, as long as he’s using it in the normal fashion, that would be considered “machmas melachah”.
-My opinion. Check it out with a certified Dayanician.