In other words, "a trick to keep from pretending to be surprised is to avoid showing genuine surprise." That doesn't make sense, and it leads me to believe the author didn't understand the definition of "feign".
It makes perfect sense. If you suppress the urge to show surprise in these situation even when you are genuinely surprised, you won't feign surprise either. She's saying 'avoid showing surprise in that context altogether'. I don't see anything in there that suggests the writer didn't know what 'feign' meant.
Also-- I do like the actual content of the written-rule-plus-oral-tradition. I think a lot of the cases where newcomers get flustered comes from genuine enthusiasm of a mentor who fails to reflect on the power imbalance their increased level of knowledge creates. A joke or affectation that would be playful between two knowledgeable insiders can on the other hand easily crush the spirits of an outsider.
The reason I mentioned it is that misusing a common term can be confusing and unnecessarily time consuming. As evidence, look at the response of bglusman above:
> It's not mentioned here, but when Recurse Center explains this rule to recursers, it's explicitly discussed that despite the name, it doesn't actually matter if you're actually surprised, it's still a "violation" of the rule to express that surprise in the particular terms of "I can't beleive you don't know about x!".
So in this case you have an explicitly written rule about feigning surprise, supplemented by an oral tradition that expands the rule to cover genuine surprise.
edit: soften, fix grammar