I saw that. It’s not FOSS, though if that’s what you’re implying.
Just reading over the license, it allows neither making modifications to the source nor commercial use. Allowing both of those would be necessary for it to qualify as either Free Software or Open Source. (And I’m not sure those are the only things in the license preventing it from qualifying as FOSS.)
Source available ≠ FOSS. And Grayjay isn’t FOSS even if its source can be perused.