I think I just expect the kart to be larger in comparison. At any rate, have you considered sizing the axle down? I'd hate to see you clip something.
Watched the video again, it all makes sense that the size is what it is given the information. Something just is playing a trick on my eyes (and I look at way too many karts). That tread pattern is what came stock on quite a few of the full suspension yerf-dog karts.