I'm not too familiar with the property in question and since the author doesn't seem to be using an agent or provide an exact unit number, it's difficult for me to be certain.
My opinion, however, based on the condo complex and the description is that $900/mo is for the entire unit. It's likely that the owner no longer lives in the property, but wants to hold onto it for future use or as equity.
I invite you to follow up with the poster directly. He provided his email in the description: firstname.lastname@example.org
All the best!
Gina Landers, Broker, CDPE
DRE # 178500375 License # 01388614