Is it at all possible for someone from Nigeria to pretend to be someone from the USA using a USA area code & phone number?

Yep.  Yesterday, I got 5 phone calls supposedly from my part of town.  Some were from the irs, some from social security and a couple from Amazon.   They ALL had foreign accents.  (I know that none of these companies is less than 2 mles from me, so being bored, I f*cked with them for a while.  Acted like I believed them, gave them a fake name and soc sec number, I acted like I really wanted them to help me solve my "problem."   Then I called them VERY dirty names.  Asked them what kind of animals they have sex with.  They called ME dirty names and hung up. 

Yes scammers use this sort of thing all the time.

That's definitely possible. Always be skeptical and know when to end all further communications with the scammers.

There is probably a computer program out there that "bumps" phone calls from number to number much like there are services that allow you to change your VPN Network source on the internet to show your computer is at random locations to allow for internet security and privacy. A VPN  number is assigned to each computer network and computers link up one to another through this network - this is how zoom works - people log into their computers and log into a zoom location and share the same computer program/file/assigned computer bank location. Your computer logged into that location is showing that computer your location at that time. A roaming VPN program could then show your computer to be at a different location using a different wifi source location when you log into the same zoom program and zoom chat room to protect your privacy - meaning a roaming VPN number SHOWS the other computer you are at a different location even if you have not moved your physical location.

When you understand how this works, it should then be easy for a hacker to use a program to bump their call from their cell phone physical location, meaning their cell phone is dialed from a physical location, but the call is first transferred to a cell phone number in the US and then transferred or repeated off a repeater then sent to your phone, showing a US number but originating someplace else. That technology is now easily out there. It happens all the time with e-mail spam using your address to send out spam that did not originate from you. So yes, such technology and programming is out there.

POSSIBLE????? this is how these thieves do business.  We have to leave one phone line open to unidentified callers, because several medical offices have their staff, working remotely, do the calls for appointment reminders, medication changes, etc.  Other wise, I block things, send repeated offenders to the DoNotCall list, and of course, extortion schemes get report to the FBI.  If somehow one of these jerks gets thru, then I also keep a painfully loud police whistle by the phone . . .

i think its possible

Test him/hers knowledge... Ask questions about the supposed location.

Yes that’s possible! Stay skeptical