When I cast Balance, I had 0 creatures in play, 2 cards in hand and 4 lands. My opponent ended up losing his creatures and also had 4 lands so that stayed the same, but he ended up only discarding down to 3. I tried to screenshot it but I only got to capture the moment after his draw step when he went up to 4 cards, then played a planeswalker. As you can see in the 2nd screenshot he has 3 cards in hand after having cast Teferi. I'm pretty sure I didn't miss anything there. The only thing that could explain it is if he activated his Staff of the Storyteller during my turn, but I don't recall if he did. If he did, well this explains that, but I'd look into it as I don't think that he did.