He probably knows Ned through Sloane! Ned also takes part in club quidditch, and he's a Gryffindor prefect the year below Wally. Ned would likely get along well with him since he sounds a bit like Sloane, but he would definitely try to be the voice of reason because he's a Dad. They'll be in all the same NEWT classes, but Ned wouldn't push him to be tutored by him if Wally felt embarrassed. I'm definitely here for future (probably a month or two) threads if you think they'd be friendly-ish.