Possibly just other usages of "im Urlaub" greater, like "im Urlaub erlebten wir das und das", "im Urlaub hatten wir schönes Wetter" and so forth. "In Urlaub" as in presently staying there, appears to be entirely Improper in Higher-Austrian, but I don't find out about the Germans. I've also heard https://bihlmayermedia-bilder.com/urlaub/wir-sind-im-urlaub/