I was on both Giannandrea's and Singhal's teams at Google (I left last year). Giannandrea doesn't really have an AI or machine learning background (LinkedIn page: https://www.linkedin.com/in/johngiannandrea). He was put in charge of machine learning relatively recently, IIRC less than two years ago. Before that he was doing Knowledge Graph - he came into Google through the Metaweb acquisition - and that technology stack really doesn't have much AI or ML in it. Google has tons of good AI people; if it wanted to, it could easily have replaced Singhal with any number of engineers with more AI experience.