Show add_meta_box by selecting a specific category

You could try this:
get the ID’s of the attached categories and wrap your add_meta_box function inside a simple test against your defined cat ID.

add_action('add_meta_boxes', 'is_in_cat_example');

function is_in_cat_example() {
    global $post;
    $category = '5'; // can be an array of ID's as well

    if ( in_category( $category, $post ) ) {
    add_meta_box(...);
        }

}