trick question, the hotel is infinite, so you can move guest 1 to room 2, guest 2 to room 3 and so on and have room 1 leftover for Sisyphus and his boulder, therefore he is indeed happy
There are conditions where an infinite hotel can "run out" of rooms. Veritasium has a great video on this. Here's the link because there's no earthly way a dumbass like me can explain it intelligibly with just words.
This would be the case if we tried to fit an uncountable infinity into the hotel. But there is only one Sisyphos and one boulder, so we can use the above trick