Ha ha ha ha ha damages the receptors in his brain! What rubbish. Did they actually say that OP, really?
Some children do 'read' well but not comprehend/understand at the same level of course and I trust my child's teachers generally with her learning because they are the experts in educating children, not me. However I had to have a chat with my child's teacher when she was still reading at a level that really was too low for her. It was a bit advanced for her age (she was mid-Y1 and it was the purple one, from memory) but they were boring her rigid and she was reading similar short chapter books to other posters children for pleasure.
Teacher told me she was already on a band that was 'too high' for her age, I was lucky she'd let her have those books and she couldn't move up. Gave me a big lecture on comprehension so I thought ok, it's likely she is right and I am wrong perhaps she doesn't fully understand the vocabulary and content.
Over the summer she had to do a 'fun project' mini book report and it was supposed to be from a list of titles. She refused to do it, read The Magic Faraway Tree and did a two pager on that. I've read that book myself - she understood it/themes/characters etc perfectly well and when she came across a word (there were a few) where she didn't know the meaning she asked me. That's how vocabulary expand,s right? You read a new word, don't understand what it means, so you find out and then you know!
They're not always right. Luckily mines got a different teacher this year. Two weeks of guided reading into term and she was two bands higher (and she got a gold star for her report).
I should add to this that my child is autistic and is cognitively advanced. She doesn't know how to begin a game with a friend during a lunch break without help, or how to not collapse into a terrified heap at an unexpected loud noise but her academics are one small area where I don't worry as she's doing really well. Before anyone says this is a stealth brag - it's not, she's v strong in one area and not so strong in another!
OP I wouldn't get hung up on scores (I don't even know what those are, I only know colour bands and I get an education age compared to actual age on her SEND reports) as I'm sure they don't mean much. I would ask them to clarify that nonsense comment for a start, and maybe speak to whichever teacher is in charge of the literacy at the school. They may be able to explain or change something. If not, just encourage him to read whatever he likes in his own time.