CSS is being loaded on all admin pages. The CSS should only be loaded on the plugin specific admin pages. You can check via using the
$pagenow global, or using the "load" hook.
BTW, another thing I ought to note is that I noticed the plugin is using a file called
generate-xml.php for AJAX calls. This is usually considered a bad practice. The
wp_ajax_ hook should be used instead for best performance and also for insuring a more secure way.