In this context, individualist and collectivist are labels that describe an agent’s preferred social arrangements and social norms. There’s nothing about keeping one’s identity small that prohibits one from having a higher priority for group preferences than individual preferences.
I don’t think Graham expects one’s identifiers not be shared with others. He’s arguing the point more in line with your first definition, in that the more aspects you add to your personal identity, the more sources of bias one must avoid. As Graham says, “all other things being equal, the best plan is to let as few things into your identity as possible.”
In this context, individualist and collectivist are labels that describe an agent’s preferred social arrangements and social norms. There’s nothing about keeping one’s identity small that prohibits one from having a higher priority for group preferences than individual preferences.