I shared a story about a boy who used to do that as he wandered around the house while Mum kept reading the book. The difference with this child was that when Mum would stop reading to see if he was paying any attention, he would comment saying "keep reading mum, I want to find out what happens next". He amazingly, was quite engrossed in a lot of the stories but obviously felt quite comfortable walking around listening. Depending on a child's learning style, will have a lot to do with where they learn best, the most comfortable position or place to be in, to successfully absorb the information.
As a teacher and strong advocate when promoting books and reading, I encouraged the Mum to try again and make it part of the daily routine. She said she would give it another go. I hope she does for the little boy's benefit, and helps him to develop his love for books.