Well I'll give you one I know: St Michael's mount in Cornwall (second in his list) is definitely not a cathedral. There is a stately home and smallish castle on a small tidal island on the site of an old monastery but I'm pretty sure it has never been a cathedral. It's not in or near a city for starters.
p.s. It's a cool place to visit btw. You can walk over to the house at low tide and then the house is on a steep hill surrounded by a lovely garden which you are compelled to enjoy until the next low tide at which point you can walk back to the mainland. Nearby is a heliport where you can get a passenger helicopter to the Scilly Isles which are also worth a visit.
This makes more sense, as castles tend to move in straight lines. As another comment mentions, if these were cathedrals that would mean a bishop in residence, and we all know bishops prefer to move diagonally.
Oh and the last one "Stella Maris monastery" is not at all connected with St Michael, which the wikipedia article acknowledges. It's just somewhat near a mountain that is in a biblical story with St Michael. "Stella Maris" means "Star of the Sea" and actually refers to Mary.[1]
https://en.wikipedia.org/wiki/St_Michael's_Mount
p.s. It's a cool place to visit btw. You can walk over to the house at low tide and then the house is on a steep hill surrounded by a lovely garden which you are compelled to enjoy until the next low tide at which point you can walk back to the mainland. Nearby is a heliport where you can get a passenger helicopter to the Scilly Isles which are also worth a visit.