The paper is wrong. The reason they say they are from Nigeria is simple - "Follow the money." Those who don't have a means of collecting money from outside the country must mention Nigeria eventually.

Those who've been in the game for a while, have the ability to collect money from any country the "victim" feels comfortable sending money to.

Also, about the intentional grammatical error. It's not intentional. Many of them aren't educated. In fact, most learn to use the computer and internet on the job.