AMD64 is the same as x86-64, just another name for the same architecture - it doesn't have to do anything with actual cpu vendor.
Quoted from https://en.wikipedia.org/wiki/X86-64:
x86-64 (also known as x64, x86_64 and AMD64) is the 64-bit version of
the x86 instruction set
.... .....
The original specification was
created by AMD, and has been implemented by AMD, Intel and VIA.
Various names are used for the instruction set; prior to the launch,
x86-64 and x86_64 were used, while upon the release AMD named it AMD64
Quoted from https://askubuntu.com/a/84775/150504
It's merely a convention due to the fact that AMD created the 64-bit
extensions to the x86 (Intel 386/486/Pentium) instruction set. At that
time, Intel was pushing Itanium as the only 64-bit solution, and Intel
didn't copy AMD's extensions until it was clear that AMD had created
something that was being used widely. The #define AMD64 was used to
distingish this 64-bit instruction set from Intel's Itanium
instruction set.
amd64