There have been threads and threads asking this same thing. All of the info they are willing to provide is in those. Here are a couple recent ones:
https://us.forums.blizzard.com/en/wow/t/please-clarify-new-multiboxing-rules/864878
and
https://us.forums.blizzard.com/en/wow/t/falsely-banned-for-multiboxing/863935
The second one is full of discussion about Joe Multiboxer.
I can TL;DR this for you very easily, though:
If you take Joe Multiboxers statement about it not violating Blizzard policy, you do so at your own risk. Blizzard doesn’t check every statement made by every software developer for veracity.