My guess: it's NOT a typo. As you state, the procedure is probably: roll a single d6, the result tells you which of the abilities recharge, thus: Recharge 4,5,6 -- on a 4, 5 or 6; Recharge 4,6 -- on a 4 or 6.
This allows a single die roll to determine if all, none or SOME of the creature's...