Great question: I've commented on it here: https://graphql-eventbus.vercel.app/docs/principles/thinking... See the "Specification for Event based communication" section.

"While cloudevents does have a promising specification, it does not provide any runtime guarantees. It's similar to OpenAPI: a specification that is hard to follow because nothing enforces runtime compliance with the specification. While this specification makes sense for public Event APIs, we believe that GraphQL Eventbus offers a lot more for building your enterprise event bus."

GraphQL eventbus does incorporate some best practices from cloudevents and event architecture in general: it creates an eventID and publish time for each event and propagates metadata like requestId.