Important to note that Walton didn't really come out of nowhere. He was a second round pick in the OHL draft (3 picks after Kevin He, as an interesting tidbit).
Apparently he would have gone even higher but his family was demanding that whoever draft him also had to draft his twin brother Conor. Sudbury complied with this request, drafting Conor in the 4th round. Then they traded him to Windsor a year later. Lol.
Anyways, the point is, he's always been a top prospect. He just fell off due to some perceived weakness in his compete level and defensive game. I'm not sure he's shown much improvement there but watching him play, he's developed some great chemistry with Alex Pharand, a fourth round pick for Chicago. Pharand is 6'3" so they both tower over a lot of the competition. They play some really beautiful offensive hockey together.