YC is looking for companies that will be home runs. The essay should have made that pretty clear! The footnote you quote is saying is that if a YC company does

YC is looking for companies that will be home runs. The essay should have made that pretty clear! The footnote you quote is saying is that if a YC company doesn't turn out to be a home run, but instead becomes a lifestyle business or a small acquisition, YC will be happy for you and supportive of your decision. This is because they are nice people who know that these outcomes are meaningful for the founders, even though they don't really have an impact on YC's bottom line. But that's not the same thing as deliberately looking for founders who are trying to build "lifestyle businesses" from the outset - in fact, that's the opposite of what they're looking for.