Seems like there's a discrepancy here.
Your Apple account password has no relation to Face ID whatsoever.
Face ID is what lets you unlock your iPhone without having to enter your Passcode. Are you sure what you were asked change was the Apple account password and not the iPhone's passcode? Those are 2 different things.
Apple will never force you to change the Apple account password or even your iPhone passcode for that matter, but some corporate or school based Exchange email accounts will place profiles and restrictions in place when added to the iPhone and those may require a regular password change as a safety measure. That is a decision and requirement of the office or school IT department, not Apple.
If you explain exactly what you actually changed and where this change happened ewe can offer more specific advice.