Maybe just other usages of "im Urlaub" amplified, like "im Urlaub erlebten wir das und das", "im Urlaub hatten wir schönes Wetter" and so forth. "In Urlaub" as in already currently being there, seems absolutely Incorrect in Higher-Austrian, but I don't find out about the Germans. I have also heard https://bihlmayermedia-bilder.com/urlaub/wir-sind-im-urlaub/