How to restrict users to view their own custom content type?
When the implementation of hook_node_access() returns NODE_ACCESS_IGNORE, it is not denying the access to a node, but it is letting other modules decide if the user has access to the node. If none of the modules implementing hook_node_access() returns NODE_ACCESS_DENY, and none of the modules implementing hook_node_grants() returns 0 for the node, then the user has access to the node.