Does he seem to be reading books at home without any type of struggle or are you seeing signs at home that make you wonder about challenges with reading?
If the issue is just at school and that he's reading at a lower level than you anticipate he is capable of, it's possible that whoever did his school testing just didn't expect him to go beyond grade level and therefore didn't push to test beyond grade level. This happened a few times with our ds in early elementary - once he was reading he was reading *way* ahead of grade level. At the end of K he tested not-so-high above grade level... after a night where he'd stayed up half the night. His teacher found out about that when I off-handedly mentioned it at pickup and right away she thought outloud, "Hey! I should recheck that reading level" so she tested him again and it went way back up to where it really was. The next year with a different teacher he was always testing as "at grade level" and when we asked if they'd tested any further were told "we don't need to, he's where he's supposed to be". So any number of things can happen with testing at school.
Re the selection of books he reads (at school or at home) - some kids don't get excited about books in early elementary, especially (just in my experience) boys. Our ds never was very interested in fiction, and the only fiction he'd read for the first few years of school was Captain Underpants. When he was in 4th grade he discovered the Ga'Hoole series and the Warriors etc, and he loved those books - but he also read through them really quickly and then was back in the zone of not having any books he was interested in reading.
Re the books you mentioned, I'm not familiar with them but took a quick look at them on Amazon - neither of them look like they are 4th grade level books (to me), but I'm not a teacher so don't put any weight at all on my opinion - that's just an observation by a mom of a former and a current 4th grader.
If, otoh, you're worried about what you're seeing at home - do you feel like he's struggling? It's not always easy to recognize reading (and other) challenges in gifted kids because of their overall ability levels. Are you seeing things at home such as struggling over words when reading aloud, reluctance to read aloud, other signs of things being "off"?
Re your ds saying he feels distracted in class - both of my dds have said the same thing. My kids were all initially in an elementary school with project-based work and they sat at tables in groups. My older dd really liked the project-based type work in spite of the distractions so with her we worked on learning how to avoid getting caught up in the distractions. My younger dd, however, is extremely individually achievement oriented and the distractions really bothered her. We transferred her to a more traditional school this year, where children are seated at individual desks and there are behavioral checks and consequences which keep the classroom overall much quieter. It's not the classroom I'd dreamed of having my children thrive in - but it's been wonderful for her - she's much happier in that type of atmosphere at school. FWIW, she's also my child who has a challenge that impacted her ability to learn to read (not dyslexia, an associative memory challenge). It went unrecognized until 2nd grade in part because her intellectual abilities overall masked it and she was reading at grade level.
My last piece of advice, as the mom of two 2e kids, if your gut is telling you something isn't quite right, listen to what it's saying. You're the parent and you're the one person who knows your child better than anyone else, no matter what their credentials may be. If you think you need to look into this further, don't be slow or afraid to look for further info. You may find it's nothing, but if it's something, you'll be very glad you didn't wait for another year or more reasons to look further.
Best wishes,
polarbear
