This is how Disqus works. Something still has to power the API that serves the data for it and we happen to like Django a lot so that's what we use. There are also a lot of parts of Disqus that are not the embed (moderation panel, account management, etc.)
The admin/crud stuff, moderation panel, account management, etc, that's what django was developed for. Great choice.
If you ask me to start Disqus from scratch again, I'd probably use django too, for the admin part, but for the API I'd go commando, closer to the metal, without framework at all. No need to load a 100MB routing/modeling/templating monster just to perform an invisible API call.
Highly optimized plain python scripts would work better.
Sometimes frameworks are more like handcuffs. Just sometimes.
(In fact almost every single project I've ever built has used Django, and there's never been a limiting factor of that choice)