That is an interesting Ghost story.

But the author cannot remember the room number?  Not when he went to change rooms later?

I seem to recall that Nana Hotel keeps your room key for you when you leave the hotel for the day, but they give you a card that verifies that you are a guest, with your room number on it, that you show to Reception to claim your key when you return.

The Author didn't keep his card either, when he wrote the story