Is mentioning something without showing it worldbuilding

[aegix drakan_v1legacy]

I would hope that it works as worldbuilding. That's one of my main shticks for the RPGs that make. >_>

Either you overhear NPC's talking about places and events and creatures, or a name pops up in an item's description, or a readable document talks about a previous event, or it comes up as part of conversation, etc.

I try my best to make it all relevant to what's going on at that given moment though, as jarringly different information can ruin a good scene.

 

[hermes]

Yes, it counts as world building, mostly by providing information about things that happen outside the perspective of the main characters/narrator. They also help selling the world as a much bigger place, not something that just waits for the hero to resolve issues.

It is not always necessary, but it helps in cases were the perspective is entirely set in the main characters (like Star Wars or Hunger Games).

 

[Glongpre]

World building usually shows how the world reacts with each other on a bigger level than individually. So if that guys sister was infertile, and that was a common thing, then that could be world building. Or if that guys sister was one of many girls kidnapped by a supposed secretive assassin sect. Or if he is trying to protect her from something specific in the world, like roving bandits, or monsters, etc.

But just to mention he has a sister is just to develop his character in that situation. It tells you nothing of the world, but it tells you something about him.