The article doesn't touch on why this is an actual saint rather than a minor local cult like Saint Guinefort[0], the saint dog[1].

The reason, AFAIK, is that the early church didn't have a process for canonization, it was just all local cults. By the time they decided to establish a proper process (proof of miracles, witnesses, devil's advocate etc) many local churches had their own saints, and they decided to basically accept all the ones already in use and only start enforcing rules for the new ones. So the idea that "there's a holy man in the east who did this and that" resulted in "eh, sure, let's write down Saint Jehoshaphat too".

Christianity-as-trivia is a lot of fun.

[0] https://en.wikipedia.org/wiki/Saint_Guinefort

[1] not to be confused with Saint Christopher, the dog-headed saint https://en.wikipedia.org/wiki/Saint_Christopher#/media/File:...