How a Y Combinator food-delivery app used TikTok to soar in the App Store

The internet trend is simple: A friend or family member looks into the camera and tells viewers, in a slightly aggressive tone, that they are about to witness a presentation and that they better be nice. 

That’s what Kendall, the sister of Lucious McDaniel IV, did, and after she stepped aside, her brother pitched his company, BiteSight, a food-delivery app that lets users watch videos of food before ordering. It also lets customers see what their friends have ordered and bookmark places to try out. The app plays on how young people engage with…