The residential status of the mooring was established in an earlier application (2006) for a certificate of lawfulness: https://planning.cheshireeast.gov.uk/applicationdetails.aspx?pr=07/0005P&query=93ae35cd-38bc-408b-a01b-d662c9b531fe
This application is quite interesting. The applicant was asserting that, because a residential boat had been moored there for over ten years, it made the whole site residential. The Council disagreed and only gave residential status to the mooring itself, not the adjoining land. That's why they started submitting applications for new dwellings, which were then refused. Then the owners have tried to find a loophole by using the permitted development regs to put up warehouse/storage buildings with a view to converting them to resi later. I suspect they've been advised that the conversion to resi will be refused, so they've decided to sell to an unsuspecting mug who thinks they can build a house there.
Bear in mind that even if conversion to resi is accepted, that's only an approved for a change of use of the existing warehouse building, which, if you look at the plans is a horrible ugly thing and not at all desirable as a house. If they try to build something new to live in, it will need full planning permission, which would almost certainly be refused.
It's in a conservation area and in the green belt.