It says 2.8 on it which is my daughter's level. She reads it confidently
Although she can read a book, it doesn't mean they are all aimed at that age range, though.
This is a series aimed at older children who read at this level. This may be that they find learning to read more difficult, or it's taking longer, they are new to English and a whole raft of other reasons.
There are a number of series of books with the same age.
Books at that reading level previously didn't have any appeal to older children. The idea of these types of schemes is to have story lines that might be more appealing for them.
I've seen similar threads with these schemes before, where they've ended up in lower primary classes instead of being in y5/6/7 classes. Some may be too scary, too dark, have more about relationships, etc in them so aren't always suitable for the younger children, even though they can read the words.