Does world difficulty change when making a new world after defeating Wall of Flesh?

So my guide NPC was killed because I thought I could summon WoF by drowning the NPC.

(I realised I did it the wrong way).

I made a new world and made a hellevator after watching the guide of beating the WoF boss, the fight wasn't as bad and it gave me the items I needed. I finally got hardmode, I went back to my main world (where I drowned the guide), and still had the items. Then I got confused, it seems I need to ask a question I didn't find online...

Does your difficulty save when going on your main world, but defeated WoF on another world?

(this might be confusing but you get the point)

Solution 1:

The difficulty of a world is world-based, not character-based. Your old world will not turn to Hardmode until you defeat the Wall of Flesh on the old world. Keep in mind that if you use the Pwnhammer to destroy Demon Altars or Crimson Altars, they will not break until the Wall of Flesh has been defeated, and will deal half of your health in damage.