The Leafs drafted centre Dakota Joshua in 2014 in the fifth round, 128th overall. He has played four seasons at Ohio State since then, and is .78 points per game player over his career there. There was no expectation the Leafs were going to offer Joshua a contract, and his rights expire on August 15 of this summer.
Generally, when an NHL team trades for “future considerations”, the return is often an AHL player from the affiliated AHL team. Given that the rights to a player who could be a UFA in a month are not worth a lot, no sensible team trades you a draft pick for them.