It's really about being a resident of a state rather than a "citizen."

But it can lead to various edge cases, some of which are being spotlighted at the moment as people move around to get out of cities.

Basically you have this somewhat odd situation where you have free movement within the country and the federal government doesn't actually care where you spend your time. But you essentially need to be a state resident for purposes of things like a driver's license and paying state taxes and some states really want your money if you spend more than a bare minimum of days in the state. So there sort of a disconnect between federal rules and state rules.