Is this lambda abstraction created as a generator of a recursive function?
If you look at the $Z$ combinator (because we're in an eager context), you have $$Z=\lambda g.(\lambda f.g(\lambda v.ffv))(\lambda f.g(\lambda v.ffv))$$

If you look at the code, we don't apply a fixed point combinator to sum, we simply apply sum to itself, so there's no reason for sum to be "generator".

You can also readily show that sum is (modulo currying) equal to $\lambda f.g(\lambda v.ffv)$ for some $g$, basically by replacing (f f ...) with (h ...) where h is the argument to $g$ in the definition for sum (minus the outermost lambda).