I don’t think this image accounts for second languages (otherwise Hindi would be twice as big), and as I understand it the reason that English is the official languae of Nigeria even as an independent country is so as not to give anyone’s first language priority over any other
I think you’ve misunderstood me a bit. English is the official language of Nigeria. One of the reasons it’s the official language was that it was seen as neutral within Nigeria because it wasn’t any group’s first language. Or it was at the time, anyway. That was an entire human lifetime ago now, so it’s quite possible that things have changed a bit since then.