Students, and others, are allowed to register to vote in both places. It's not really the same test.
The hotel analogy does work, because it is largely the same test. If the hotel/marina leases a specific room with no rights to change the room/mooring then council tax would be due. If they retain the right to move people around, then there is no council tax, but the marina/hotel pays business rates.
So it depends on what rights the marina has. Given they presumably don't have planning or rights to provide residential moorings, I'm sceptical that any of the boat owners would be able to pay the council tax even if they wanted to.
Therefore, it is perfectly possible he slept 3/4 nights a week in each place, was allowed to register to vote in either place, needed to do some laundry fairly regularly and broke no rules. Dan Neidle admits this in his comments section, but he's little more than an influencer who needs clicks, so doesn't point this out anywhere noticeable.