This wasn't the reason why the law was pass, the government has been looking for means to legalize cryptocurrency for the long time and small small them been dun they shift their view on cryptocurrency from being negative to positive and also looking for means to tax companies that they can tax to make some revenue from these companies them.
This is also my thoughts, the Nigerian government like many other government won't make any law that won't benefit them. The Nigerian government has seen that no matter what they do crypto-currency is always ahead of them now they are trying to accept it only just for their benefits.
There are a lot of Crypto-currency linked businesses, companies and organizations in Nigeria and placing a tax on Bitcoin activities will surely rack home good profit for the government, for me it is not becoming a case of if you can't beat them you join them and find a way on how it will benefit you and this is the vibe the Nigerian government is giving off.