Does every speed run have to be on nightmare difficultly?

No, it can be any

Normal is recommended for most, as it is usually the fastest.

Ok thanks, i wasnt sure since it seemed way too easy

If you want to do a speedrun for the in-game leaderboards, it has to be nightmare, however. But for speedrun.com, it can be any! :-)

Yea thats why i was confused.

Hopefully I helped!! :D