I don’t think you understand it correctly though. That would be correlation, not causation. The “stressful environments” is only one of the by-reasons they give for the behaviour, while urging people to remember that you can’t use the study to conclude things like “true equality of the sexes and a just society would mean the elimination of homosexuality”, which is just sort of the same logic you use, just the other side of it.

Adding the bit I’m referring to:

But there are things that are completely unique to modern humans, who have a complexity of sexual orientation and preference that we do not address at all," he said.

The study also warned against “misinterpretation or misuse of our findings,” such as “a misguided notion that social equality might eliminate” same-sex sexual behavior in modern humans