The problem is that beneath the feigned outrage, everyone can see that this is just a stupid bully of middle manager making a stupid decision. Nobody really cares enough about it to actually change real-world plans.
The second point though. This must have come from higher up. I mean, I doubt that manager was actively watching Twitter so this must have been identified by some automated system and trickled to the manager as a notification...
Many scenarios are possible, and we can't expect easyJet to air their dirty laundry, so we probably won't know exactly what. What is completely inconceivable is that there is a company-wide policy that came into effect (and was subsequently immediately withdrawn this morning) to hunt down and deny boarding to passengers that criticizes easyJet on Twitter.
I wish it actually amounted to something. They probably won't get any drop in ticket sales, because in cheap airline market you pretty much don't have many (if any) alternatives. People are still going to fly with them because they're the cheapest / only ones flying to the destination they want.