The video gives you all the information you need.
Because of the move from the bike.seedhost server to the ant.seedhost server (see article Migration from SH3 to SH2) the url bike.seedhost returns a error 404 when trying to reach it. Because of that the isos of July can ONLY BE INSTALLED if you have NO INTERNET.
For the ease and comfort for our users an earlier build and release was needed.
Hence we decided to do a holiday release.
That is why the release has the number v21.09.8.
The advantage is that you have the iso with the LTS kernel or Long Term Support a month earlier as well.