That installer contains intel (x86_64) binaries. The behaviour of platform.machine() and platform.processor() is expected, due to Rosetta the binary runs as if it is running on an Intel Mac.

There is a "universal2" installer for Python 3.9.1 which will run natively on Arm systems.  The experience with 3th-party packages ("pip install ...") might be a bit rough though: this installer variant is quite new and I expect that most packages with C extensions do not yet have binary wheels for this variant.