This is the reason why it's best to keep private all our crypto transactions for security purposes since we don't get full support from the government once crypto transactions is being mentioned. Nigeria will be closing lot of opportunities from crypto which most of the countries who have accepted bitcoin today are currently enjoying.
Keeping private gonna do nothing though, I think the nigerian bank could tap into the account and search for information where the money that got into that account comes from, if it's from exchange it could be very obvious, I doubt they could detect p2p but money transferred from an exchange is easy to detect I guess.
Hopefully though they could somehow find a way to overcome this act of banning that's just done out of ignorance against crypto.