It's certainly confusing as presented, both for MIT-plus-restrictions, and the dual licensing.

For a lawyer's opinion on those two things, see:

https://writing.kemitchell.com/2022/01/21/MIT-for-Noncommerc...

https://writing.kemitchell.com/2023/09/10/Two-Kinds-Dual-Lic...

Kornel is also behind the DSSIM library (in Rust), which I've found useful for comparing images before and after compression.

https://github.com/kornelski/dssim

Fun fact: I wrote DSSIM as a development tool specifically for pngquant, because I needed a way to measure improvements in dithering. Classic per-pixel algorithms only saw it as added noise.

And the excellent Mac OS image compression utility ImageOptim: https://imageoptim.com/mac