"What is, is legal" isn't all that useful. The restrictions were short-lived; anybody who would have tried to get standing to contest them would have quickly found their cases tossed as moot when the restrictions were lifted. Short-term injunctions might have been granted, but showing sufficient loss to merit an injunction would have been difficult.
There was differential outrage and indignation here when one state imposed restrictions (or required quarantine, hardly enforced on the traveler), and justification when another state, for the same reason, imposed the same restrictions. So attitudes and from-the-hip responses are sketchy.
There's some Federal case law guaranteeing freedom of travel between states; it was a right given in the Articles of Confederation, not in the Constitution (but then again, most assume it was deemed unnecessary given the tighter relationship between states). I'd argue that it would be a right assumed since guaranteeing natural rights by not limiting them was what the Constitution was all about, with the Bill of Rights deemed a mere spelling out of some of the more prominent rights that a citizen had by virtue of being a human (with all due caveats for limitations on women and the not-free or unpropertied), which the government didn't provide but merely was to not limit. But all rights are subject to "compelling state interest" restrictions.
Courts have been hesitant to overrule restrictions on travel or commerce when they involve public health, and for that there are a number of cases. As long as the travel restriction was based on established state interest and based on reasonable criteria, limited in time and extent, then I doubt a judge would do more than toss out the case.
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