Pop was once a shortening of “popular,” but it’s now a specific genre – peppy songs about love and having fun.
Motown was considered pop in the 60s, but it’s not now. It’s purely R&B, which is pretty much a genre of black artists, with a focus on ballads.
The redefinition of genres is common. I remember someone here categorizing the Grateful Dead as country – a definition that would have gotten nothing but laughs, scorn, and odd looks back in the 60s and 70s. But country has changed since then and calling the Dead part of that category is not out of the question.