Not sure what kind of toilet that was....or if it was a holding tank or a septic....
Not a plumber, but the only toilet that dumbs directly down into a tank can be only found in travel trailers, airplanes and busses.....it dumps into a holding tank and these things do not have man holes to crawl into...septic tanks do, but they are not located under the toilet as a general rule...certainly would be illegal in any jurisdiction I have worked in....lol, so are direct dumping johns unless it’s a portapotty....so my guess is.......that the guy was in a porta-potty......a not uncommon effort by some crazies..
I see this was in a park......Some parks have permanently installed porta potties that are serviced by a sucker truck on a weekly schedule...they are in all respects a outhouse. There is no toilet.....just a seat and a big hole or two or three.....lol