The Bolded line is the line that it refers to:
$return .= '<span class="cbSnglCtrlLbl">'
. '<label for="' . htmlspecialchars( $inputName ) . '" class="checkbox-inline">'
. '<input type="checkbox" id="' . htmlspecialchars( $inputName ) . '" name="' . htmlspecialchars( $inputName ) . '" value="1"' . ( $value == 1 ? ' checked="checked"' : null ) . $attributes . ' />'
. $label
. '</label>'
. '</span>'