Yes, that is METAFONT.

You'll find it more accessible via METAPOST, and there have been font designs made using it. Better starting link is:

https://davidcarlisle.github.io/uk-tex-faq/FAQ-mfptutorials....

See “The Concept of a Meta-Font”: https://gwern.net/doc/design/typography/1982-knuth.pdf

Not the OP, but probably (please correct me if I'm wrong...) Knuth's claim was that a font's metrics could be described as geometric transformations and equations. I believe most of the TeX typefaces were described with Metafont.