I guess you're wondering about that simply because you have your own definition of "chubby", which seems to be along the lines of "not thin, slightly overweight"
For the average chubby chaser I'd say that the first guy you posted is probably considered as borderline not chubby (i.e. not chubby enough).
In any case, when uploading torrents people are free to choose any category anyway. There's not really any line to be drawn, to be honest. Every one may have a different opinion on what category is best, but overall categories do a pretty good job at helping find what you like