Sorry for the "pregnant pause" - technical glitch...
Let's say the DM puts a trap with a poison needle in a dungeon, then a rogue tries to pick the lock and gets pricked resulting in his death... Hey the rogue just participated in worldbuilding because he discovered that if there's a trapped lock(element A) and it goes off while he is picking it(element B)... he might die(revelation about the world). Am I misunderstanding the definition here? If not then what is the difference between building the world and interacting with it?
No, I don't think you're misunderstanding, but you are maybe seeing only a part of the picture.
If the above scenario happens, the players may, indeed, have discovered something about the world - that there are poison traps, and they kill! But the chances are good, in my experience, that this will not be new knowledge - it will already be known (or, in poor cases, merely assumed) by those playing. Often, they will be somehow implicit or explicit in the text of the rules. As with exploring the real universe, things can usually only be discovered once - at least by any one group of people - because the second and subsequent times they go there we don't call it "exploration" or "discovery".
Since game worlds are not real but imaginary, any "discovery" is actually "building". Thus, if the GM has decided/discovered/built something in advance, sharing it is not "building" since it's not "discovery" (the discovery had already been made). Likewise, if the player decides some "unique thing" or background for their character, it's "built" as soon as their decision is accepted into the world model - the timing of which relies on the authority allocation parts of the game rules. In 13th Age this is not 100% clear; do the players have
carte blanche, or does the GM "vet" every element, and it only becomes "real" in the game world when the GM agrees? For me, it's
carte blanche, and that's the basis on which I like 13th Age, but the rules text allow it to play either way.
When the player-defined elements of OUT and background come into contact with the GM's world elements, that is when in-play discoveries that are guided by both GM and player can arise. The role I see Icon relationships playing in this is to constrain the GM to actually include situations where those OUTs and backgrounds are going to come into focus, so that joint discovery about what they mean is possible. That's all. It's not a big deal, in the greater scheme of things, but it means that the player's desires concerning what aspects of the universe they want to prod and poke at to see what comes out have mechanical support (and, perhaps more to the point, mechanical memory prods) that the GM is directed to use.