The choice_id is hexadecimal, but the submit for checkbox selected validate for string

The choice_id is set as hexadecimal, but in the submit for checkbox selected validate for string.
When the choice_id is 435268284 which is hexadecimal, not include letter, the is_numeric function will return true. Then the submit value will not work

function advpoll_checkbox_selected($choices, $votes) {
  $selected = array();
  $count = count($choices);

  for ($i = 0; $i < $count; $i++) {
    $choice = strip_tags($choices[$i]['choice_id']);
    if (isset($votes[$choice]) && !is_numeric($votes[$choice]) && !empty($votes[$choice])) {
      $selected[] = $choices[$i]['choice_id'];
    }
  }
  return $selected;
}