Modern SPA frameworks are usually built on components. You can combine components to define a tree of elements that represents your UI. This pattern is also often referred to as a Declarative UI pattern.

GraphQL works well with declarative UIs, because you can define fragments and combine them to create queries that best match the data the current set of components you are loading require. In this way, it's flexible in a way REST isn't (at least typically) and syncs well with Declarative UIs.

I can't speak to datalog though.

He's talking about the recommended use of things like React or Elm. React will probably have the basic info that ties it to GraphQL the closest, given the creators.