Yep, I found the source by searching for it on Github, what I was calling out was the fact that a link to the source from the Flatpak website itself was buried at the very bottom of the "about" section where I missed it completely the first few times I went over the site. It should have been included in the "Build" or at least "Developer" section of the site.

Maybe it's just an oversight on their part, but I find the lack of any discussion of source or licensing (is it GPL, MIT, BSD?) on the site a bit of a put-off. I see from digging into the Github files it's LGPL, but why not advertise that, and the source link, more prominently on the main page? That, along with the other issue I mentioned (catering to only a few distros while claiming support for all distros) gives me pause.