I read that as a reference to the shapes of the glasses, not their volumes - some beers come in stemware, some in cylindrical tankards with handles, some in slightly fluted glasses or ones with a bulge around 2/3 of the way up etc.
In Canada, there is technically a legal definition of a pint (568 mL, 20 imperial fl oz) - but it is a rare bar where you can ask for a pint of beer and expect the glass you receive to contain 568 mL of beer. Most bar owners seem to think “pint” just means “largish glass of beer,” being in practice anywhere from 15 to 22 oz. There is certainly no requirement that beer glasses have volumetric markings on them.
