It's kind of a meme mode. You can tell because of the random size changes they slapped onto bosses.
For The Worthy is not just size changes tho.
It changes some of the bosses attacks aswell in addition to giving them increased damage beyond any reason and HP bloating them.
List of changes to enemies , bosses , world in FTW
Secret world seeds are world seeds which have been discovered as secret easter eggs that generate worlds with strange or unique features. Unlike regular world seeds, which affect only the usual world structure, secret seeds can produce worlds with characteristics that would not be attainable...
So yea kinda true Master Mode is on that "meme" seed.