That's one example of a nonlinear function, yes. You also have (eˣ)/(1+eˣ), or (e²ˣ-1)/(e²ˣ+1), or a host of others which don't contain anything if-like at all.
> These were not AIs but rule-based systems with if elses.
I believe I already made my point with the ReLU example, if you don't want to concede it that is also ok.