He was a YC partner. He no longer is. And there's a difference between an equity partner and other types of partners. But again, YC is incentivized to let in companies they believe will deliver the most total value to the YC portfolio, so admitting Luke at the expense of another founder who was better qualified is directly contrary to their interests. Also, the YC batch sizes aren't fixed, and they have wiggle room. To avoid the conflict, they could just admit one additional startup who would have otherwise been cut.