Probably a part of it, but I did not submit my site there directly at least. I think they used different sources to seed the list. There was a very active thread on HN about two or three years ago where very many folks shared their personal websites and from that several OPML lists where compiled. I noticed quite an uptick in feed subscribers around that time.

Also by the way, Henry Desroches, the author of the article we are discussing in this thread, also maintains a web directory personalsit.es, where I had submitted my site as well, so that might have also been a source for the kagi small web index.