Wizard's 2 dice staff attack
 

One of the NPC wizards in the Adventures has a staff that does 2 dice of damage as a free action up to 2 hexes away.

This is above and beyond the Staff V capability, of which the staff does 1+2 damage.

Is this a special magic item or an error?

There doesn't appear to be errata for any of the Adventures.

Re: Wizard's 2 dice staff attack
 

This is Adventures 2, page 2/10 "Seshua Herm ST 20 ... Weapon: Staff (2d)"

This is a mundane attack. At ST 20 his one-handed staff damage is 1d+4, which has been converted to 2d in this case. Using his Staff V occult attack he only does 1d+2, as a free action, that ignores armor, but this would cost him a point of fatigue or mana.

I'd like to add the occult attack after a comma in the weapon listing, but that's not the spec.