The official story is that some witnesses were running HF20 already, and a specific transaction didn't comply with HF19; that being the new code allows upvotes during the last 12 hours, and the old code does not allow that; and that caused the blockchain to stop producing blocks because of that bug. Witness servers had nothing to do with it.

I have no reason whatsoever to question the official story since everything done on the blockchain is open source and too many Steemians are IT experts who would have blown a whistle if they believe it was done on purpose. I don't see how it could have been done on purpose to affect the price of steem. It was simply a coding error which happens sometimes, and they did an excellent job getting the blockchain to work properly again as quickly as they could while keeping everyone informed on Discord and Twitter about what was happening.