Not really a flat tracker in the American sense of that term.
In Japan they have a strange form of motorcycle racing they call "Gamble Racing" because people are there to bet on the riders, much like a horse or dog racing track. Riders are sequestered in a closed room before their race so no one can influence their mindset or bodies before the upcoming race. The bikes are weird contraptions and when I was in Japan during the 80s, they used vintage Brit engines: BSA, Triumph, etc., from the 1960s. Hopping-up the engines was minimal because the gaming people didn't want any one rider to have an advantage and the tracks are all-paved. It's essentially a "spec racing" series similar to Formula Ford or Formula Vee.
ps. My guess is that this was some sort of exhibition/challenge to help sell tickets.