I believe Nylander terminated his contract with MODO some time around the draft, and then the Leafs loaned him back to MODO after they drafted him (although I can't find any record of this now).
Yeah, I don't really understand the timing of it either. He still has another year left on his SHL contract, so why bother to sign him if he's going to stay in Sweden? Since his ELC won't slide, it just wastes the 1st year, and makes it less likely that the Leafs will get some nice NHL production out of him in the 3rd year of that ELC. If they're signing him now, I'd hope it's because they want him on the Marlies next year, but even then I don't really like the move. The Marlies are going to be full of wingers, and he'll probably get the same treatment as Kapanen/Timashov/Johnsson, starting on the 3rd/4th line and working his way up. IMO, it would be better for him to stay in Sweden and play 2nd line minutes and special teams while working on his offensive game than it would be for him to come over and play 4th line minutes for half a year before hopefully working his way up (no guarantee he gets more ice time though). It's not like staying 1 extra year in Sweden is going to hurt his development.