Why are YOU the one who has do this??? Obviously, this is a job from a programmer!
As far as I can tell, HTML is simply a language that defines which and how the various elements will be displayed on the page. HTML lets you choose any given URL to display something in an iframe, but HTML isn't used to define what the URL will actually be. Whoever wrote the code probably used some other language to determine the video URL. I don't see why the programmer didn't think it was easiest and best to simply copy the same URL specified by the person making the post.
Anyway, the "Match URL" code is probably being used to determine if the URL comes from one of the acceptable websites on the list. It looks a little bit like Regex (which I do have some experience with). Regex would look something like this
.*anondrop.*
The above Regex code basically says "look for any URL that has the word (anondrop) somewhere in middle of the character string." If so, the URL is a positive match and you can embed the video. Notice that your Vimeo Match URL has the word "Vimeo" included in a rather complicated character string. Likewise, your Youtube Match URL will look for URLs which include "youtu.be/youtube", etc. In the past, Youtube had other URL formats that still work today.
In any case, you need a direct link to play an anondrop video. The file id is part of the URL, but the URL has to end with a filename and an extension. We need to know what language the programmer used to write the code, so we can figure out what command will let you specify the correct URL.