Most dictionary's define a "landing" re flying, as
Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground
Ground also refers to water in other dictionary's. A "T&G" is also a "landing" As both of these normally require the aircraft to cease flying albeit still moving, I presume that full or near full power would be needed with balloon tyres in the oggin to keep flying, so neither should be called a landing.
Possibly trespass occured? but not a criminal offence (unless covered by some act like railways) Assuming no breach of the ANO occured ie 500' closer etc,, Then whats the problem, skillful flying but a bit daft as anything there, like floating detritis could have made it more than a prank.