CBN never told that Nigerian people cannot do trade Bitcoin or cryptocurrency, They just prevent people to use Bank account for doing crypto related work. They have taken the tricky path to harass trader and maybe they attempt to take control over traders and attempt to regulate cryptocurrency trading. If they do not allow traders to use bank accounts to take payments then how can they say that Nigerian Residents Free to Trade BTC!
So basically they can trade but they can't withdraw their crypto in banks from what I can understand, this is a pretty vague and scummy stuff for CBN to do, I mean this restricts traders their way of getting the profits that they gained in the process. P2P could be a solution but there is a rampant scams going on with P2P so it will be difficult.