[Cybiote]

Adding a little to your wonderful post, another possibility for why the conflation of the original lisp as based on the lambda calculus is that its notation was heavily inspired by the lambda calculus, even though it was more properly a refinement of the μ-recursive functions (of form f:(N,N,...N) -> N) over the natural numbers.

While a lot of people are trying to defend the lambda calculus as a basis, I think this actually undersells the significance of LISP. Apart from Lisp the language family and its implementations, there is Lisp, (arguably) the first practically realizable mathematical model of computation. That is, it stands on its own as a model for computation†, continuing along a long line of which I think Grassmann's 1861 work on arithmetic and induction is a good starting point.

Turing Machines are intuitive and the lambda calculus is subtle and expressive, but Lisp's contribution was to place partial recursive function on a more intuitive/realizable basis in terms of simple building blocks of partial functions, predicates, conditional expressions and symbolic expressions (ordered pairs/lists of atomic symbols). Lambdas come in as a notation for functions with a modification to facilitate recursive definitions.

†Making Greenspun's Tenth Rule trivially true.