Wasn't his main roster debut against John Cena?
Like, I know he went back down to NXT after that, but to me debut means the first time you've appeared on the main show. Using football as a comparison, you've got the u18s and u21s teams, and then the first team. So say Billy McBloggins comes from the u21s to play one game this year for Warchester Rovers, then he's made his debut. Sure, he might not start playing regularly for another couple of years, but that one game is his debut regardless.