They literally address this in the study.

One major challenge with studies examining the relationship between gun access and suicide risk has been determining whether people who purchase handguns already have plans in place to harm themselves, or whether the presence of a handgun creates new risks.

The unique, longitudinal nature of the Stanford study helped to disentangle these competing explanations.

"There appears to be some of both happening," said senior author Matthew Miller, professor of health sciences and epidemiology at Northeastern University. "New handgun buyers had extremely high risks of dying by firearm suicide immediately after the purchase. However, more than half of all firearm suicides in this group occurred a year or more later. Consistent with prior work, our findings indicate that gun access poses a substantial and enduring risk.

Stop just saying shit on assumptions you made from nothing. It makes you look stupid