Mauritania deserved to qualify based on the quality of their 2 goals against Angola alone (they lost, but still)
They deserve to qualify based on their performances in general, unlucky to concede a last minute penalty against Burkina Faso. Today, they were better than us too. Solid defensively and deadly on the break, they'll surprise whoever they get in the next round.
I think it's a good thing in general for African football as it shows the traditional weaker teams are getting stronger, long gone are the days of the 5-0, 4-0 group games in the AFCON, last Afcon felt like the beginning of that, the smaller teams have only gotten stronger since.
Edit: Namibia is another one to look out for tomorrow.