When a tourist from other worlds spawn in the one im currently playing, they keep their orignal casual outfit, but the rest(formal,sleepsuit,...) will be randomized as if they were a generated npc.

This is normal. Tourists are mini-sims, with only some of the data of their complete versions back at home. So any data that doesn't come with the mini-sim, for example other outfits, will be generated at random as necessary.