I know Vercel uses AWS Lambda's behind the scenes to process web requests at least. I'd assume caching is also handled through Cloudfront by default. The place I currently work uses Fastly for caching and Vercel for hosting and it's definitely caused some issues(and much finger pointing on both of their sides) when one of those services makes a breaking change.
Perhaps they're using CloudFront and providing an end user CDN on top of it. Both are partners with AWS. Both were multicloud, and it seems, aren't anymore.