you have to live and work in Nigeria for a while to fully understand how utterly corrupt and venal every level of Nigerian society is. Everybody is only interested in themselves and will steal anything they can, and are continually on the look out for opportunities to scam each other.
Having lived and worked there for over 8 years (does that count as "a while"?) I would say that statement is a simple/sweeping generalisation, and that there are large numbers of normal honest people there for whom this is untrue!