A soft fork only requires a majority of witnesses to run the code in order for it to work.
This soft fork had a supermajority, however. And the support for it extended well beyond the consensus witnesses (top 20). At the time of the fork, only two top-20 witnesses were opposed - one of them (clayop) disabled their witness, then making it 19/20 in favor of the new version.
Brother tarazkp mentioned 17/20 top witnesses and you are saying 19/20 who is right?
17/20 are needed for consensus to implement a hard fork.
This soft fork (any soft fork, actually) only required 11/20, but it ultimately had 19/20 when it went live, plus many backups.
Thanks for sharing this information