Strangely....when I first got interested in computers the box with the "system" in it was the CPU, everything else was a peripheral. Yes, that was back when even a mini-computer (DEC PDP-11) still needed it's own room and dedicated AC for cooling. But that persisted as the PC worked it's way onto everybody's desktop.The box with the "system" was still the CPU even though it had the drives, controller, I/O and display all inside it on ISA cards. Only the printer, monitor and keyboard were considered peripherals. It did cause confusion for us uninitiated when the geeks were talking about the awesomeness of the (8086) CPU that was inside the CPU.
Semantics
To be fair they still call the "box" part of the computer (to distinguish it from the whole system) as the "CPU" where I live. The actual CPU (the "Intel") is called "processors" instead. Depending on who you talk to, CPU and processors can mean entirely different part of a computer.
It's similar how they call GPUs as "VGA", any kind of storage whether HDD, SSD, or flash drives as "hard disk", UPS and / or stabilizers being called "stavol" no matter the brand, any type of display connectors as "HDMI" even the VGA or Displayport ones, calling all types of memory cards as "SD card", "headset" as a blanket term for any kind of sound devices you stick in or on your ears, and all sorts of misnomers in the realm of computing. That's just how it is.
And don't get me started on them calling anything involving LED llights as "RGB".