Thanks Robert

The game used to be called "racehorse keno". I knew that, but didn't really know why so I asked google. There's a nice explanation by John Grochowski at the attached link.

Here's the most pertinent part of his answer:

Like bingo, keno is derived from the Chinese Lottery, and its lottery association is what led to the racing connection. In the early 1930s, bingo halls in Reno started offering keno, but lotteries were illegal under Nevada law. To sidestep the issue, the game was named “racehorse keno,” and each of the 80 numbers was attached to the name of a racehorse.

So it stood until the 1950s, when Nevada introduced a new tax on off-track horse race wagering. Casino operators didn’t want any confusion about what was and was not subject to the tax, so they removed the horse names to leave a game strictly by the numbers.

And here's a link to the whole column that he wrote :

http://grochowski.casinocitytimes.com/article/keno-and-horse-racing-63339

I bought some used keno tickets from James Campiglia, which included the tickets that I show from the Cotton Club and the El Rio. This ticket was in the group also...like the Cotton Club, it shows horse names. Since there's no club name on the ticket, I don't know where it was used.