Heroku is just an easier way to deploy to servers. It doesn’t scale down to zero, scale up as needed, etc. You still have distinct servers that you know about, can manage. S3, Fargate (Docker), DynamoDB, even SNS/SQS are considered Serverless by AWS’s nomenclature.
It doesn't scale to zero, but the article was about how much more it costs running only serverless 0-24, but how hard it is to fiddle with Linux/deployment/CNAMEs/etc. (Especially that they have constant load, 10+M req/day.)
And so it seems to miss the obvious middle ground between raw EC2 (or Elastic Beanstalk managed EC2) and full on-demand Lambda, which is modern managed hosting (PaaS, Deis/Dokku/Heroku).
AWS Fargate is a compute engine for Amazon ECS that allows you to run containers without having to manage servers or clusters. With AWS Fargate, you no longer have to provision, configure, and scale clusters of virtual machines to run containers
