That makes no sense whatsoever. Even if Williams decided they had a problem with every single one of their manufacturing managers (itself quite unlikely...)
1) Why did they not have deputies who could step up in the emergency?
2) Why would they all be released simultaneously? It would take an incredible coincidence or conspiracy on the employees' part to all have firing cause simultaneously, even if a review was involved, and mere bad performance would result in retraining or warnings, not sackings (unless every single one of Williams' manufacturing team leaders is new, which is unlikely). And if a conspiracy was evident... ...What. Were. You. Doing. Team. Leaders?!?
3) Why did the bosses think they could maintain work restrictions on sacked personnel? While it can happen in the UK, a sacking makes it less likely, since it would be more difficult to prove the company was harmed by the staff working for rivals if that company decided they were harming the company's interests by continuing employment with them. (If The Judge misunderstood and this was actually voluntary encouragement that happened to be wildly successful due to team poaching/low morale/great offer (in the latter, expect them to show up at Racing Point and/or Renault because they've been hiring for those positions recently!) rather than legal termination of position, this can be skipped).
4) Who tries giving new contracts out - especially with employee-disfavourable terms - when two other teams are on a recruitment march and there's known to be unusual amounts of disruption in their own team? The carrot is better than the stick in this situation. I'm not sure who is the direct line manager of these manufacturing heads, or who wrote the new contracts, but they should probably be sent for retraining or warned...
5) I've been in a work-to-rule environment recently, and it is not fun. Even (or perhaps especially) if you're one of the people who thinks the cause of the protest is silly and refused to have no part in it. It's not just the lost hours that will have cost Williams, it's the drag of being around moany people who can't be trusted to pull their sleeves up and don't dare display enthusiasm at anything, all in fear of being called a "scab", "loser" or a "teacher's pet" if they look like they care about work. This does not appear to have anything to do with a union's opinion of such conduct; the union recognised by my company was cautiously disapproving of the latest work-to-rule system, has warmly approved some in the past, and it was the same bad atmosphere either way.
So, I feel sorry for the people who just want to put in a good day's work and give Williams a decent racing car. Depending on the exact situation, I feel sorry for those who felt wronged, too.