I think there must be some difference between US English and English English here. In English English " I am at the same hotel" is perfectly acceptable, but not to Duolingo.
It's more common for US English speakers to say "at the hotel" than "in the hotel" also.
I'd imagine you would say this to someone on the phone who you can't see but is in the same (insert place) as you. May somebody please add to my post? ¡muchísimas gracias!