I don't know which Reddit thread you're reading (there are many I'm sure) but the one in r/Aviation seems to have a favourite theory that there was a credible threat of someone with MANPADS, which are shoulder-launched surface-to-air missiles and not some sort of sanitary product.

Apparently they have a ceiling of 18,000ft which is exactly the limit of the restriction in El Paso. Aircraft are allowed fly over if they go above that

That's also just the cutoff for class A airspace. I think people are reading too much into the specific height.