Macaulay Culkin didn’t reveal what exact role The Big Bang Theory wanted him for, but it sounds like he was being considered for either Sheldon or Leonard.
The premise of two nerds and the pretty girl does describe how The Big Bang Theory kicked off with Penny moving into Sheldon and Leonard’s apartment.
This was clearly not a premise that appealed to Culkin, and it wasn’t the math that threw him off.
It also sounds like he didn’t get a lot in the way of details pitched to him.