They always have been active participants on the forum with lot of recognized members which has helped them to get their own local board but also impressed by how active they are with such good number of posts within a month while some big boards are not having that much forum engagement.
Given the Nigeria's population (more than 200 million, 6th most populous country in the world) and more importantly how popular bitcoin is there, its not really a surprise that they are climbing up the lader fast and I wouldn't be surprised at all to see them at the top in the future.
Success of the Nigerian local board should be a proof enough to forum staff that it makes sense to create few more local boards to those who consistently have good numbers, namely Pakistan and Bangladesh as their numbers would most likely grow too if given local boards.