Strictly, MetaPost is not Knuth's. It is a derivative of Metafont, but is different. I keep meaning to learn to use it, and keep failing. So huge shout out for getting this posted!
That it is a language somewhat designed to solve linear equations is something I have yet to really wrap my head around. I want to say it is far far more descriptive of what you are drawing than something like SVG. That said, I'm not clear if I could justify that claim.
I see that you are right. I skimmed the wikipedia article about MetaPost, and Knuth's name caught my eye more than "derived from".
Metapost was first released in 1989 by John Hobby in who was also effectively a coauthor of Metafont. I will say that the MF language is really kind of a delight. It has a clear influence from TeX in its macro construction, but the presence of first-class variables which TeX lacks makes it a more productive language overall.
I was a bit inspired by it when I took my one and only CS class as an undergrad. One of the few homework assignments I actually turned in was supposed to be a simple calculator with 26 assignable variables (A–Z). I thought that was boring, so I let variables be of any length and turned the calculator into a linear algebra solver so if you wrote, e.g.,
it would give you the values for X and Y that met the constraints. I got a C on the assignment because the TA didn’t understand my code (written in CWEB and presented as a 20+ page source listing alongside the functioning executable).