In-built Wlan and and/or Rfid chip.. they are out to get you!
OT.. similar experience here.. i got an older Apple mini PC from 2012 or so, it was wiped, even had a new hard disk. So it was not even mine before.
So i started it up without network cable, had to enter new name, password, then it asked for my "Apple-ID". I have one but pushed the "later"-button.
So the thing starts, my real name and "Welcome" properly displayed at the upper right and asking if the proposed Apple ID was mine. It was.
Even with built-in WLAN this thing should not have been able to get to my router without entering the router's keycode. Hmmm.