They are not the same chip.We have no way to know if that’s true. (Also: there is increasing evidence that the A14 and M1 - at least the SoC chip - are essentially the same).
Also, the evidence is directly from Tim Cook‘s mouth, when he said that they we’re developing a new family of processors “ specifically for the Mac.”
The “M” series is specifically for the Mac. Not for the Apple TV, not for iPads, not for any other weird products you can think of, just for Macs.