Grotesque in the context of typography is a category of sans serif typefaces, specifically the one from which typefaces like Helvetica descend (they are usually called neo-grotesque). So the GP joke is based on a double meaning: on a first read it may seem an insult, but typographically he is just stating a quite obvious thing: that Helvetica Now is a grotesque typeface.

The alternate name for Helvetica is "Neue Haas Grotesk".