Showing only posts from the current user who is logged in?

The variable is not valorize: $current_user->ID is 0, so the query extracts all post, try to give it a non existent integer value

Try to substitute $current_user->ID with

($current_user->ID==0) : -1 ? $current_user->ID

It assign -1 to the author, if there is no user. So the query must return no results!