Earlier quoted context omitted.
Chronological is still fits the interface of a recommendation algorithm. You can take HN as an example of a recommendation service - while they remove things that are off topic, you'd have to argue that YC endorses whatever is in the #1 spot on HN.
Who is "they", though? Aside from the spam filters, posts largely make it to the front page (or not) due to community moderation. YC isn't the one making those endorsements, the moderating population of HN users as a whole are doing so.
HN has more active, hands on moderation than most social media sites, and there's a stronger argument that dang "endorses" the front page of HN than that Steve Huffman "endorses" the front page of reddit.