This is true, the crawler actually waits for your content to render, and yes, if after N time there's still nothing rendered your site will not be indexed properly.
Regarding the issue you had with Github Pages, it might be that Github could be interfering with the crawling process, since your page is under the github domain (unless you're using a custom domain). OR your content was just taking too long to load :)
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
This is true, the crawler actually waits for your content to render, and yes, if after N time there's still nothing rendered your site will not be indexed properly.
Regarding the issue you had with Github Pages, it might be that Github could be interfering with the crawling process, since your page is under the github domain (unless you're using a custom domain). OR your content was just taking too long to load :)