Ps/2 doesn't always mean external device. Even in my own HP Elitebook, the device settings show the Keyboard as PS/2 keyboard. That's just the way it's listed.
Check 2 things:
go to HP Driver Downloads for the HP PB 65606
Select your operating system and download the latest drivers for the keyboard. Secondly, see what language is set. Control Panel - Region and Language -> Change Keyboard.