The content itself is NOT FOSS- it never was. Otherwise, I'd have already gotten it long ago. I just finally got to install and start playing this classic back several days ago, having purchased it for $6 on GoG beta test.
And, the link you point to indicates that they're aware that GoG is making the game available and is a means for which you can obtain the assets proper. Considering the Installer does some fetching of "proper content", including enhancements, that's not a good thing as the enhancements weren't approved by rights holders. Moreover, the link you provide indicates to go looking on a known abandonware site or on a torrent for the content to play. Even worse.
We need that like we need a hole in our heads, guys.