There's nothing improper about calling it Apple Silicon. Yes, the chips have ARM-based CPU cores, but those cores are designed by Apple, not Arm, and they're only one part of the overall A-series and M-series designs.

Apple, by the way, was a co-founder of Arm and helped develop ARM processors for use in the Apple Newton. Its early work on making ARM CPUs highly power efficient paved the way for their now-widespread adoption in mobile devices. There's some irony in how a part of the Apple Newton reverberates throughout the industry today.