[Ancapistani]

I hate to be that person, but neither the article nor the study makes that claim.

All we know is that people who visit the ER or who are hospitalized "for cannabis use" (not defined in the abstract; full text is behind a paywall) end up with dementia at a higher rate.

That does not mean cannabis caused it. They've accounted for many confounding factors, but you can't account for all of them. Off the top of my head, perhaps people who are in the very early stages of dementia do not tolerate THC as well? Maybe their emotional regulatory ability declines before diagnosis, and they're therefore less able to bring themselves down if they experience anxiety.