I think that binance add NGN because Nigeria is open for new technologies and does not make unnecessary problems (good for them) rather than they have dominated the industry. Just loock at NGN/BTC volume. 26 M NGN - that's 75 k $. Its nothing. I know that its first day of trading but its less than noticeable.
It still contributes though, and saying that
it's nothing is like an understatement considering that Nigeria is one of the most progressive countries in Africa despite the fact that poverty still runs out and about. Seeing that Nigerians are actively engaging in trading cryptocurrencies, it's already a good thing and something worth noticing and worth mentioning since that side of the map often is disregarded on economic scenes.