preg_match() versus is_numeric()

xmlsitemap_output() uses the following code, where preg_match() is used to verify if the parameter passed to the function is a number.

  if (isset($chunk) && !preg_match('/[0-9]+/', $chunk)) {
    // ...
  }

It would be better to use

  if (isset($chunk) && !is_numeric($chunk)) {
    // ...
  }