I just raided the project git repo and there is definitely no common lisp in there. Unfortunate name clash!
- https://github.com/asdf-vm/asdf/issues/383 - https://github.com/asdf-vm/asdf/issues/547
They did do something to ameliate this though: now they refer to the proect as asdf-vm as much as possible, to distinguish it from Common Lisp asdf.