Universal Videogame List - www.uvlist.net

They are not the same thing. Ping Pong is used for table tennis games and is a subgenre of sport. The question is if the tag "tabletennis" would be better than "pingpong" here.

Pong is for all games based on the Atari game Pong.

So I should go in and change the tags to tabletennis and change all the pong like games to a pong tag? leaving nothing in the pingpong group?

No, these "mass editings" can be easily done by me.
We have just see if we prefer to use pingpong or tabletennis.
Pingpong sounds more international, less tied to a specific language. Don't know the other countries.

I think the issue is with some games being mistagged with pong instead of all pong games being that :)

Also, the ping pong tag group has existed for some time now, I think (to which I recently added the table tennis synonym).

Edit: though there doesn't appear to be any games tagged with pong...

Hmm... yes. No games tagged with pong. I wonder why. It's a good tag and there are quite some classic pong clones existing.