It does a learner no good to hear that you are shocked by a skill deficit. If you're planning to be around people who are in a learning space, you should not be surprised if they don't know something. And even if you are surprised, it is kinder to not show it.

I don't think this rule is universal. If you're in a professional environment where, say, you're coding C++, and a new collegue with five years of purported experience claims to have never used a pointer, it would be okay to show surprise. And then maybe speak to your shared leadership chain. Learning environments are special that way.

Even your "calm" version probably doesn't need to exist. If there's something they want to do and they're asking you about how to do it, by all means, it may be relevant to tell them that learning a new thing would potentially help them.

Otherwise maybe worry less about what other people should or shouldn't know.

However, the rule is really about not doing something that makes others feel bad about not knowing something or asking questions, like you said. The “No feigning surprise” phase has been a perfect hook to get people to read and understand what it means.

In some environments, feigning or exaggerating surprise really is abused as a social status and hierarchy establishment trick. Those who use the trick are trying to turn a question or gap on someone’s knowledge into an opening to elevate their own status, often in front of others. If you haven’t seen this trick used (abused) then you’re lucky. In my academic and early career I was in some environments where not knowing something was an invitation for the vultures to circle and try to turn the situation into a show of their superiority on some imagined social hierarchy. It sucks. I suspect the Recurse Center introduced this rule after having a person or batch of participants who started doing this, because it’s really toxic when it is normalized.