Head injuries cauing mental disabilities?

So quite a few times this week my daughter who is 6 months old has fallen over and hit her head on our carpet floor. She only cried for a few seconds and there were small marks but nothing serious. My aunt watches her during the day and I told her what happened. She told me that an infant should never hit their heads because it will cause them to be mentally disabled. It made me upset that she said that and it kinda made me feel like a bad mom. It also had me wondering if that a lot of people actually think that a child hitting their head will cause them to be mentally disabled. I believe that genetics and environmental factors cause those types of disabilities, but my aunt really thinks otherwise. What do y'all think? Do you think it's genetics and/or environmental factors? Or do you think it could actually come from too many head bumps?