my money would be on gear down and locked on short finals. Reasons: Pilot would not continue to land if he knew he had a gear problem. Twr has full view not many metres away to his left . He would not give landing clearance without actually looking at aircraft as he said it. He certainly wouldnt give landing clearance if he saw the gear wasnt down. He didnt appear to have a high workload at that point, just 521 and 565 landing, FDB taxiing etc. We are not even sure whether there was an aircraft immediately ahead of 521 who had to clear the runway before Twr could issue landing clearance to 521.