I think the author is misremembering Wolfram's claims. I recall attending the first open demo of SMP, where Wolfram (and I think co-author Chris Cole) were demoing it in a large Caltech lecture hall. Here's what I recall.

They had tried to use Macsyma for their physics work, and found experimentally that it was too slow on what they considered to be "medium" problems, and could not handle "large" problems at all. They were trying to do things that were pushing the limits, and pushing them hard, of what could be done on the hardware of the day [1].

They showed some benchmarks comparing SMP to Macsyma using the kind of problems that had arisen in their physics research. For "small" problems, SMP was a bit faster. Maybe 2 or 3 times or so faster.

For "medium" problems, it was 100 times faster.

And it could do "large" problems.

I don't think I ever heard Wolfram say anything about Lisp being 100 times slower than C in general. I only heard claims like that when he was talking specifically about building systems like SMP, and was comparing basing such systems on top of a general purpose high level language (Lisp) vs. basing them on something built and optimized specifically to support a system like SMP.

[1] The SMP work was done on CITHEP's (Caltech High Energy Physics) VAX 11/780. I was an undergrad at Caltech at the time, working part time at CITHEP as a system programmer and admin, so knew many people involved in SMP development and got to watch it as it progressed, and then was put into production by working physicists.