I'm guessing that it's a way for them to test if ads have been loaded after initial scripts have run, but I'm not going to dig into the code.

Honestly, the whole ads thing is missing the point. If you desired a public video hosting platform, that needs to be a tax-funded commons. Video hosting and streaming is very expensive. Similarly, users should be donating to keep Lemmy going:

https://opencollective.com/mastodonworld

https://patreon.com/mastodonworld