Not sure why you're so insistent on this when Pulumi folks themselves on this post have said that they contribute back up to the AWS provider source repo (1).

Maybe not all their providers utilize Terraform, but it was definitely how their product started out. When you run Pulimi using their AWS provider and get errors at runtime, some of those are verbatim Terraform errors.

Their docs and site is very clear to muddle this connection but if you ever used their API, you'd know this.

(1): https://news.ycombinator.com/item?id=37081306