They didn't address the confounding variable that these disorders are caused by dopaminergic issues, which are present even before becoming floridly psychotic. High levels of dopamine = low levels of arousal, so the slight elevation caused by tobacco smoking is probably pretty appealing.

Only first person experience, here, but I can say antipsychotics (which are dopamine-receptor antagonists... hence the "thorazine shuffle") cause these bouts of sedation that are made much less uncomfortable by simply having a smoke.