Cezanne had at least six years of classical drawing instruction, where you begin by drawing various geometric forms, move on to making sketches of plaster statuary, and then finally draw from the model. It's a highly technical form of training akin to doing scales all day long on a musical instrument. I'm sure there's a folder in some archive in Aix full of extremely boring and careful studies he did at the time. I've linked the one example I could easily find online above.

Saying Cézanne couldn't draw is a glorious form of missing the point, like saying Stravinsky couldn't hold a tune.

There are perhaps other qualities in Cezanne's paintings, but PG is far from being the only person who considers Cezanne's drawing skills quite deficient.