I just read the Billboard piece and I think you've got the answer, K.M.
Chuck Johnson says he became GM of the Mexican AMs in November of 1965, but didn't "initiate R&B programming until July 15."
The playlist is dated January 10.
So it was a mockup. Maybe he used it to pitch potential advertisers, or maybe L.A. stations for brokered time, which, I understand was his primary model. And if that's the case, there may have been other similiar playlists printed with a different L.A. station in that center top position.
If anyone knows Lee Tucker, he's the ARSA member who posted this XEGM/KFOX-FM/XEWV list. He's posted as recently as this January, and posted the list in question on April 8 of 2020.
In fact, we had a post here at RD last year about XEGM from a member using the screenname Multiplex, which said, in part:
Full thread here (I let him know that Tom has not made his real name a secret):
https://radiodiscussions.com/threads/xeau-xegm-etc.771004/
One last bit from ARSA. There is only one other XEGM survey there, from October 24, 1966, four months after the Billboard piece:
View attachment 9280
It shows only XEGM and XEWV. This chart was contributed by Gary Pfiefer.