I'm a little bit uncomfortable with that heuristic because sometimes things literally are absurd. I think in this case though, Bill Maris is literally not in a position to say whether they are coming in at half the value of other players. He probably doesn't know, or at least doesn't have as many data as Paul Graham.
From the article: Google Ventures managing partner Bill Maris blasted back, telling BI that Graham's accusations were "patently absurd."
First example from http://en.wikipedia.org/wiki/Non-denial_denial#Types: Characterizing a statement as "ridiculous" or "absurd" without saying specifically that it is not true