> doesn't breaking down pectin result in methanol?


Yep, but that is going to happen wheather you ad pectinase or not.
The yeast will break down some of the pectin themselves.

That is why you need to age wine. During aging alcohols combine with
acids to form esters (compounds that give wine fruitty aromas). This
is why (along with slow oxidation of tannins and other compounds)
wines "soften" with age, the harsh edges round off.