That seems to be the finding here though there is very little to go on in the article. Were the high income people not wealthy or a mix? Were the wealthy people high income, higher income or lower income?
Living paycheck to paycheck is likely stressful at any income. Having wealth likely less stressful at any income.
If you're making 500k and living paycheck to paycheck, that suggests some insanely expensive habits, there's something wrong if you don't have the self-discipline to get a bit of financial leeway at that level.
Either you're spending like there's no tomorrow, or you've over leveraged to try and live like someone wealthier still. And the actual material difference is in diminishing returns territory at that point, so there's got to be a psychological driver there.
Living paycheck to paycheck is likely stressful at any income. Having wealth likely less stressful at any income.