A more universal way would be to get the thumbnail via oEmbed API.
//second false skip ACF pre-processcing
$url = get_field('videos', false, false);
//get wp_oEmed object, not a public method. new WP_oEmbed() would also be possible
$oembed = _wp_oembed_get_object();
//get provider
$provider = $oembed->get_provider($url);
//fetch oembed data as an object
$oembed_data = $oembed->fetch( $provider, $url );
$thumbnail = $oembed_data->thumbnail_url;
$iframe = $oembed_data->html;