You're right; it could quite easily have been Futura. I think I jumped to the conclusion that it wasn't because the first Futura-alike I looked at on that site was PL Futura Maxi, which lacks the backwards-S question mark, so I assumed that was a point of distinction between Twentieth Century and Futura. But all the other Futuras on there do have that question mark, so yes, it could perfectly well have been one of those instead.