I wonder how the "rooms" are counted. I would guess that there are three guest bedrooms, but there are other rooms associated with the B&B (laundry/utility, guest bathrooms, etc.)
If there are three guest bedrooms, but the other definition of "room" is broad, thirteen wouldn't seem unreasonable.
Generator room; solar atrium; battery room: that is three + the 3 guest rooms etc you mentioned.
And thanks for bringing up laundry & kitchen. What about water?
If they were so off the grid that the cost of running poles was prohibitive, then they must either have a well or cistern system, and at least one pump, and believe me, pumps eat power!