…Japan began denying visas to Mexicans on arrival.“Denying visas…on arrival” doesn’t make sense; you’re supposed to obtain visas before you come. In fact, what happened was that Japan temporarily suspended the waiver of visa requirements. Given the disproportionately high incidence of reported cases in Mexico—just imagine the likely extent of unreported cases—it is not unreasonable to resume visa requirements; air flights between Mexico and Japan continue.
I think this was an honest mistake on Saletan’s part, not carelessness. Note that the NYT report that he links to in order to back up his claim makes no mention of Japan at all. The writers of the NYT must have excised the (likely slightly incorrect) reference to Japanese action after they found out that they were wrong. Even newspapers sometimes alter their online articles without any notice; this must have been one of such cases.
Online sources are tricky, and there’s not too much the sources themselves can do about it.
As of this post, Saletan has not corrected his report, though that is not my point here.