Possibly just other usages of "im Urlaub" elevated, like "im Urlaub erlebten wir das und das", "im Urlaub hatten wir schönes Wetter" and so forth. "In Urlaub" as in already staying there, appears completely Erroneous in Upper-Austrian, but I don't understand about the Germans. I've also heard about "auf Urlaub" https://bihlmayermedia-bilder.com/urlaub/wir-sind-im-urlaub/