It certainly shows that he's got a good sense of perspective re: drawing bodies. And that's the suggestion Paul's making, right?, that Cezanne makes stupid goofy mistakes. The sketch here is just a sketch, but it shows he knows his shit.

Sorry, but no. Left arm (right from the observer's POV) is orangoutan-sized, while the other (closer to the viewer) appears too small and thin in comparison, even accounting for perspective. Hip bone goes way too high, and thorax is amorphously portrayed in comparison. Neck starts behind guy's back. Head outline is missing.

The thing that bites guy's ass is ridiculously sized if a lion was intended, and that front leg looks more human than animal (then again, he might be going for some mythological chimera-ish thing).

Overall, the drawing is confusing and I can't make out what many of the lines in the legs/ground area are supposed to represent.

Finally, this is not a casual doodle. Lines were drawn and refined several times over. If he was going for manierism or El Greco-ish stylization, fair enough, but still proves little about his ability to draw. If he was trying to achieve a render true to anatomy and perspective, I call fail.

I don't know whether Cézanne could draw or not, but I don't think this works as evidence that he could.

Cezanne can't be blamed for the lion. This is a drawing of a statue in the Louvre. The sculptor may have made the lion small intentionally. But the human was pretty anatomically correct as far as I remember.