In American English "apartment" almost always refers to a single residence in a large building. The large building is often called an "apartment building."

The phrase "the vast majority of apartments don't have to pay energy bills" sounds like a claim that each apartment (i.e. each tenant) doesn't have to pay their own energy bills, because it would be very odd to refer to an entire apartment building (or the building owner/manager) as as "apartment."

It's poorly worded, which is causing a lot of confusion.

The full comment does provide context clues to the author's intent, but it was somewhat poorly worded (i.e., "vast majority of apartments" is easily taken to mean individual units/their tenants, and not the property in the aggregate.)