Or it might be just one of the things that he likes so much that he can deeply focus. This is quite common.
DS#2 had about 13 "obsessions" before leaving home, from Ghostbusters, to juggling, to cycling. We once "had" to take him to see the MIT juggling club perform in a snowstorm. Reading was one of them, too, particularly, long, difficult books about history, politics and war, which probably led him where he is today: USMC.