I don't understand what you mean by "better-quality studies" (in the context of this study).
It seems to me that you're really looking for follow-up studies.
This study "assessed the association of sedentary time with leukocyte telomere length (LTL)" [0] - that's it.
Investigating causal relationships would be another study.
You're right about alternate interpretations/speculation, though.
We need better-quality studies to draw conclusions about causality. A correlation is just a correlation.
I didn't read the original study, so I don't know if it drew unwarranted conclusions about causality, but the Science Bulletin article certainly implied them.
I'm not clear on what assumption you are claiming I made. My point was about quality of evidence (see, e.g., [1]). Observational studies are considered lower-quality evidence than randomized trials.
This study "assessed the association of sedentary time with leukocyte telomere length (LTL)" [0] - that's it.
Investigating causal relationships would be another study.
You're right about alternate interpretations/speculation, though.
[0]: https://academic.oup.com/aje/article/doi/10.1093/aje/kww196/...