It doesn’t necessarily tell us that for sure, but it supports that hypothesis yes. And there’s some behavioral data out there from before this study to support the idea:

https://pubmed.ncbi.nlm.nih.gov/29887035/

But there’s also still the decrease in glutamate release in some contexts too. A lot more work has to be done to figure out what the 2 opposing systems are doing and how it ultimately could contribute to depressive-like behavior (or not).

Always take everything with a grain of salt (skepticism is part of good science), but there have been associations between chronic marijuana use and depression. Whether habenula is involved or not remains to be tested.