In an interview, Moriyama claims to have never bought a camera for himself. All the cameras he uses have been given to him. He loves compact cameras for their convenience and fluid style of shooting. The documentary about him shows how he strolls around, aiming a Ricoh GR at something but not even using the viewfinder.
I love his work. It sounds like he's had a hard life as well, some issues with alcohol and other substances, not to mention being poor, but he's clean now and still working. His book 'Memories of a Dog' is superb, and describes his attempts to use photography to capture his life, and recapture memories from his past. I get the feeling that a reasonable amount of his work involves going to old childhood haunts and exploring places he once knew.