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.,

    2X+3Y=14
    X-Y=1
    X
    Y

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).