In the Greyhawk Supplment, Men are listed as getting 1 or 2 attacks

Here's something I never noticed in Greyhawk before. Men are listed as getting 1 or 2 attacks, unlike humanoids. As far as I can tell this is not explained anywhere. It could be reference back to the Chainmail "Weapon class" rules for Man-to-Man Combat.  If so though it should really be "1 or 2 or 3" per Chainmail, page 26. Also, it should apply to the humanoids if they are using weapons.

What is more likely is that it is an early reference to a rule change for Berserker. In OD&D Vol 2, they just get a single attack at +2 against normal men. But in the Monster Manual this was changed to 2 attacks or one at +2 to hit; thus their attacks are listed as 1 (or 2). So possibly Gygax was using this rule change at the time of Greyhawk but forgot to explain it in the text.