flapping hands indicate autism?

After reading an article... it said that if a child enjoys flapping hands (repetitive hitting movements), it's one of the signs of autism. Is that true... I sometimes see my child doing movements like that. But he's only 7 months old? People around me say not to worry too much because he's still a baby and still exploring his motor skills. But as a mother, I'm really worried. Any advice or anyone have similar experiences?