The author says the opposite:
"The non-recursive way is more efficient as the CLR does not have to keep pushing and popping its call stack (which is quite slow). The non-recursive way is unfortunately harder to code. So the challenge was on!"
"The non-recursive way is more efficient as the CLR does not have to keep pushing and popping its call stack (which is quite slow). The non-recursive way is unfortunately harder to code. So the challenge was on!"