I've always ignored things like this and I think you should, too. What would the consequence be?! (Nothing.) They can't punish you for not making your kid read books far below his level. If there's a book log, just substitute what he actually read. I would also write something like, "he independently reads Y, which is X levels over the books you sent home, so I had him read books that are an appropriate reading and interest level." (In case you don't know, you can check reading levels at Scholastic Book Wizard.)
When my dd was in K, they had her reading new reader books for the first couple of MONTHS while they assessed everyone. She was horrified and embarrassed. Finally, she had enough, and she led a bit of a mutiny, telling all the kids that they were reading baby books and that they shouldn't have to read "baby books," which she always said with disgust. Of course only a few kids could actually read the books, but the teachers didn't want them to think the books were for babies. So they reluctantly created a reading group for my daughter and two other girls, who were also good readers. The same thing happened when they sent home "sight words" for her to memorize. She was so embarrassed at having them. When I complained to the teacher, she told me she was required to send them home, but that I could do with them what I wanted (we turned them into spelling words).
