Cannot block access to nodes with hook_node_access_records
Blog post needs to be updated. I remember having discussion with him about it.

hook_node_access is a deny access; grants are if a user has any matching grant, they have access.

you can use the alter hook to remove undesirable grants, but doing custom access requires a lot of testing and thinking. Also, read the https://api.drupal.org/api/drupal/modules%21node%21node.module/function/node_access/7 node_access documentation/code