Historical Connection: There was indeed a YMCA presence at Guantanamo Bay during the early 20th century.

So what?

There's a McDonald's in Chubbuck, Idaho. If someone writes A song about McDonald's. That means they know about Chubbuck, Idaho

Or is it more likely, like most Americans, I had never heard of Chubbuck Idaho until I just looked up locations in Idaho.

This YMCA served the needs of military personnel stationed there, providing facilities for leisure and morale boosting

This may all be true, but why would the songwriter know that.

The song is about having gay sex in YMCAs.

Here's an oral history of the song. The record producer who came up with the idea was a gay Frenchman who never ever heard of a YMCA.

https://www.spin.com/2008/05/ymca-oral-history/

we were leaving a photography session on 23rd Street. Jacques Morali saw the big pink YMCA on 23rd and asked, “What is this YMCA, anyway? “And after laughing at his accent, we told him the Y was a place where you could go when you first came to New York when you didn’t have any money — you can stay there for very little. And of course, someone joked, “Yeah, but don’t bend over in the showers. “And Jacques, bless his heart, said, “I will write a song about this!”

and

I joined the McBurney YMCA on 23rd Street. I took Jacques there three or four times in 1977, and he loved it. He was fascinated by a place where a person could work out with weights, play basketball, swim, take classes, and get a room. Plus, with Jacques being gay, I had a lot of friends I worked out with who were in the adult-film industry, and he was impressed by meeting people he had seen in the videos and magazines. Those visits with me planted a seed in him, and that’s how he got the idea for “Y.M.C.A.” — by literally going to the YMCA.