Actually the explanation is wrong.

not()

is actually

not ()

not is a keyword not a function.

Boolean of empty tuple is False and then not negates it.

I explained it better here:

https://lemm.ee/post/61594443/19783421

No it's not, "" (a null/empty string) is the parameter. Not every function needs a parameter to be valid, and negation is one of them. Negating nothing is something, so "not()" = "not(null)" = "not(false)" = "true"