I can hold a pen and pencil the same way, they look pretty much the same, and they were designed for the same purpose. So they’re the same thing, except for the important functional parts.

The upper assembly is completely different. The lower half - including the hammer, which is kind of an important part of the fire control group - is not fully compatible. Neither of these rifles have a “recoil control system”, and neither originated the concept of a buffer spring.

The FAMAS (after a few revisions), along with every other modern NATO rifle uses the same magazines and ammunition. Being designed to a set of standards for the sake of simplified international logistics during wartime doesn’t make the 416 design a “variant”.

Also we’ve designated a tractor, a tank, a 37mm cannon, a landmine, a .22lr survival rifle, and an Italian shotgun the “M4”, and that’s just the U.S. military.