As posted by one of you above, similar embodiments have been around for some time, actually the early 1970's. Questions posed or implied seem to have easy enough answers.
1) Why compromise the entire plane to build it around one perceived advantage? You don't have to. Joined wings can be used in many configurations, and choice need not be pragmatic. The hobby is supposed to be fun.
2) Why isn't the wing braced or joined at the fuselage to take advantage of the lightness and rigidity such a configuration? Perhaps root bending moment isn't a problem for him. It would be possible to do so, but probably choice of the pusher prop got in the way. Anyway, it appears that the designer just wanted to try an ideal and see what results, in this case to have wing, "stabilizer" or second wing, and vertical stabilizer from one continuous surface. What's the harm in trying something interesting that one likes. At least he's not as foolish as some aviation pioneers and experimenters, who did themselves in through sheer ignorance - and that includes at least a couple modern people/groups with history and engineering backgrounds that should have guided them away from disaster. At least this guy has a fairly large RC rig. The question for me is not so much why he wants to try this, but whether he has scaled the dynamics like volume, area, power, loadings, speed, etc. to an educated compromise, or just built a big model. Designing traditional cruciform vehicles has its limits in holding interest, without some new goal or material to study.
A little adventure is a good thing.
SK