Why does current_user_can(‘edit_posts’) return true, but current_user_can(‘edit_post’, $post->ID) returns false?

I have a plugin with a custom post type (with 'capability_type' => 'post') and a custom user role (test_user). When I check if a user is allowed to edit a post (of the CPT and which this user created) with current_user_can, I get different results when using edit_post and edit_posts (with the s).