And how they suppressed the e-mail notifications to the (real) owners about the move of the org?

That part reads really fishy.

Someone answered my question:

https://news.ycombinator.com/item?id=28795775

That seems very strange given the fact that GH sends otherwise mails for almost everything done there if you didn't disable it.

Someone else noted that it may only send emails to the person that kicked the process off.

I don't know, I don't own a GitHub Enterprise to try.

Is it possible that anything which @dnfadmin is an owner of is automatically migrated by GitHub the moment it becomes an owner? Maybe they never realized that what happens?