Instead of:
$categories = get_the_category();
$categories_id = $categories[0]->cat_ID;
…use:
$categories = wp_list_pluck( get_the_category(), 'term_id' );
Now you can correctly use in_array
to search all the post’s categories, rather than just the first:
if ( in_array( $thisTrueCat->term_id, $categories ) ) { ... }