Senegalese DNA

My children are half Mexican and my son's DNA (haven't had my daughter tested), showed 2% DNA from Senegal.I was looking at the Ancestry website and reading how that is the most common African DNA.NOW...I have to use this to help me. I am fairly certain the African DNA is not from my children's Casillas line (their paternal grandmother) but it could be in the Rodriguez line (their paternal grandfather.) I have that line in the Ahualulco area. Wondering if anyone else has had any success in tracing their African ancestry in Mexico.
Katrina Link