Wpdb->query result show 1 but is not an integer

Question

I found the solution.
The result 1 for my query means true and it’s a boolean so

$wpdb->query can return true, not only int|false as it is written above the public function query : wpdb::query

PHP code

$res = $wpdb->query("ALTER TABLE " . $table_name. " ADD " . $column_name . " varchar(35)");
error_log( $res );
error_log( "bool ? : " . ( is_int( $res ) ? 'true' : 'false' ) );'false' ) );

output

1 [18-Dec-2017 17:10:10 UTC] 1

2 [18-Dec-2017 17:10:10 UTC] bool ? : true