Because cutdowns hadn’t happened yet, at the time of the trade, the 1.01 pick you were trading for was technically “next year’s first.” So we would go by future draft pick rules, which are that the future years must all be an even swap.
If you had traded away two players for one player, that could be considered different. But because you traded for a draft pick that didn’t exist yet, that’s a “future draft pick” situation.
EDIT: It’s confusing because on the surface it would seem that you would need to send your last pick to Mundi to balance it out, but you sent two players instead of any draft picks. That’s why you got Mundi’s last pick back.