*Motherfucker* is a normal word in the USA. You can call an adult or a child a motherfucker. It's part of their everyday language. However, for people outside the US, it's offensive.
Bruh Islam was so full of shit. He knows exactly what it means, he hangs around Americans all the time, he knows it didn't mean anything about his damn mom. He was just playing dumb to stir drama and push numbers up.