I don't think that this is true, except perhaps indirectly. According to Duncan McGreggor's wonderful (and very well researched) "Hidden History of Lisp"
https://blog.lfe.io/excerpts/2015/03/27/1101-the-hidden-orig...
McCarthy was interested in computer intelligence, logic, and mathematics. Shaw, Newell, and Simon, at RAND and CIT, were already working on exactly these topics in their Logic Theorist project, using IPL, an ugly language that they designed, and ran on one the first digital computers, called JOHNNIAC - after John Von Neumann.
I you are interested in just how ugly IPL(V) was, you can see more of it than you'll ever want to here:
https://exhibits.stanford.edu/feigenbaum/catalog/ff363pt6522
Ugly as it may have been, IPL language did exactly what McCarthy wanted, and introduced the concepts of list processing, symbols, and recursion. But, a bit to your point, it's ugliness, being akin to assembly, was exceedingly off-putting.
A couple years later, at MIT, McCarthy (who was simultaneously and coincidentally playing around with lambda calculus) and his students (most centrally, Steve Russell) figured out how to do list processing etc in a much simpler syntax.
Still, the "modern" homoiconic Lisp of s-expressions was a bit farther down the line, as it was originally conceived with M-expressions, which were a bit more algol-like. S-expressions were initially just the data representation. Russell realized that the s-expression syntax could be used for both.
Thus the birth of Lisp, probably the world's most influential and enduring programming language. Sorry, this got a bit off topic.