The Grief over the use of x64 for AMD64 or X86-64 is based in the prior use of "x64" for the DEC Alpha architecture in the hardware naming: "DECchip 21x64" [0]

Digital was earlier to market the Alpha as a 64 bit ISA than either Intel's Itanium ( IA-64) or AMD's x86-64 which is also called AMD64 [1]

[0] https://en.wikipedia.org/wiki/DEC_Alpha

[1] https://en.wikipedia.org/wiki/64-bit_computing

My understanding is that these were never just called "x64" though, or at least not commonly.