In the world of football any thing can happen, an underdog can come out victorious at the end. I wouldn't write off anyone though. Nigeria is the strongest in Africa but they failed to qualify. Anyone who is able to qualify is worthy and should represent the continent. We just have to support them and wish them well.
Nigeria isn't the strongest county in Africa continent neither are the weakest. When it comes to AFCON competition, Egypt are the strongest after winning it a record number of seven and even won it for three years straight (if I'm not mistaking). For world cup competition, Senegal has gone the farest more than any other African nation. The highest Nigeria has gone is the round of sixteen which they usually end up getting knockout by Argentina.
In the knockout qualifiers Nigeria wasn't the strongest opponent, Ghana has a number against Nigeria. In all their head to head meetings, Ghana has the highest number of win as they always found a win to win Nigeria so their win wasn't a surprised as well.