My bad. Yep, you are correct. I thought the GPL actually prevented you to sell compiled version of a GPL FOSS software (Outside of the original maintainer) but it seems it isn't compared to this one which force you to keep it free. There's also limitations on what you can remove so yep. Non-free. Seemed a bit Counter-intuitive to me in the first part. https://www.gnu.org/licenses/licenses.en.html

I should probably suggest the GNU Foundation to check this license to compare it, as I often see question of FUTO software license online.