No, but I do believe that complex issues with many factors can be boiled down into simpler averages. Besides, “stress” is just as multifaceted of an issue as anything else! It implies nothing about the root causes.

Moreover, this research article did not say “if you have kids, you will be miserable”. That is a personal choice you should make for personal reasons. Some people are happier with kids! But it’s also true that childless adults are on average happier.