We are trained to distinguish one condition from another even when they look alike.
In this case, a simple history showed that baby was taking iron supplements which could explain the black stools.
Always see a doctor
Check by all means, but understand that to properly interpret what you read, you will need a health practitioner to help explain it to you.
If you are not convinced with what a doctor says, you can request or see another qualified doctor.
One example is aprokodoctor.com. Written by healthcare practitioners including myself.
Don't take one article written by Nkechi on Facebook and disturb doctors please