Human are incredibly adaptable when we are young and it’s not uncommon for young kids who need to have a portion removed (often for epilepsy or other neurological conditions) or are born with parts missing to have very few, if any, major limitations compared to the average person. Every once in a while, I’ll come across a story about an older kid or adult who gets a head MRI or other type of scan for something and their doctors discover that they are missing parts of their brain. They just never had any big issues that would have prompted a scan before then. It must be so crazy to just find out one day that you’re missing a significant portion of your brain… Anyways, I guess my point is that it’s entirely possible that the kid in your story was indeed missing a portion of their brain and the mom was just misinformed or otherwise clueless about it. I’m still choosing to believe that she was making it up though; perhaps as a more unique and “impressive” alternative to whatever condition her kid really had. That scenario is better, because I would tend to hope that a parent in her position would be able to correctly name the portion of their child’s brain that was missing…