Hey there,
This is because your video is 640 x 360 so that is low resolution.
With regards to the aspect ratio, your video is in HD aspect ratio but somehow there is a problem with your setting in Wistia because when I visit the embed URL in a new window, it is still the same (see http://prntscr.com/4u2gk7. For that, you might want to use Wistia oEmbed instead of our embed shortcode.
Thanks.