Science

The study is massively confounded. Did exercise cause good sleep, or did good sleep provide enough energy to do exercise?

They have not found evidence that doing exercise even when you are exhausted from a lack of sleep and are struggling to do everything else that has to be done will cause you to sleep better. They haven't done a study which can find causal effects, only associations.

I don't think it is bad advice; for people who are struggling to sleep well enough to keep up with the demands of daily life, trying to find the time and energy for more fresh air and walking is very unlikely to do any harm.

But, it is harmful to imply that people who are struggling are struggling because they're lazy when it may well be that they appear lazy because they are struggling. Doctors are already fucking terrible for this kind of thing and doctors who do research should not be presenting it this way when, if they are qualified to do the research, they know they have not defined the causal pathway or even the direction of the causal arrow.