I think the emote was actually originally named after the literal 90s game pogs, at least that that's what the old writeups suggest. The gootecks guy had recently done and won a goof video about playing pogs with some other streamers when the emote was first introduced, so it was named pog champ after that happening.

The play of the game thing also makes a kind of sense as a post-hoc rationale though, since the emote was used for the exact kind of surprise/excitement that you'd expect after seeing some crazy play being pulled off.