The core engine of pulumi doesn't and has never used terraform. Some cloud providers make use of terraform providers and the pulumi-terraform bridge. All the large cloud providers (AWS, GCE, Azure, K8s) now have what we call native providers which don't use any part of terraform.
@billowy-army-68599 wrote a blog about this literally this weekend:
https://www.leebriggs.co.uk/blog/2021/11/06/pulumi-faqs.html