I assumed that was more based on cultural norms than LW norms. Generally people don't discuss their IQs in polite company (or potentially-high-variance-IQ company, maybe), especially high IQs, because of the risk of being seen as bragging about something that other people may not view as high-status. In discussions outside LW I've heard people be somewhat condescending toward people who even admit to having gotten their IQs tested, as it's often associated with intellectual pretension. (And, in turn, being seen as claiming high status in a way that actually marks one as low-status is associated with social unawareness.)