This seems like an instance of a common tactic (or problem, depending on your perspective) that is especially common at software firms where management learn to work around employees' problems instead of challenging them to improve.
The engineer in this case had an emotional control issue: they reacted badly to anything new, even if they had no rational reason to do so (they were fine with it later). This could have been tackled by working with the employee to get them to understand that this type of loud public reaction is causing problems for everyone, including the perception of their own skills, and that they need to learn how to take a deep breath when a new change is announced - maybe wait a few minutes to write down what they wanted to say and then wait a few days before hitting the send button. Lots of approaches. Instead everyone else adjusted their behaviour to avoid tackling the underlying problem.
The manager’s new tactic seems to me both more effective and kinder
Maybe I'm just some asshole manager but I never saw it that way. You externalised one person's problem onto the whole team, who now all have to be aware of this special exception. Most obviously it makes it difficult to have brainstorming sessions, or if someone comes up with a new idea half way through a meeting unexpectedly, they can't raise it there and then, they have to wait for the meeting to end, pre-brief this one guy, let him/her get over it, then raise it with the rest of the team.
So whilst it may have been kinder to that one specific person, I'm not sure it was kinder to everyone else, let alone more effective. Especially because once such a culture is embedded, sooner or later half the team has some weird quirk that everyone is expected to work around or ignore.