Squad's* terms cannot bind any person who has never agreed to them. If I take some artwork licensed under CC-BY-SA 4.0 and use that art in a KSP mod, the mod is "Adapted Material" and in turn bound by the CC-BY-SA 4.0 license. Copyright law let the original artist impose terms on the use of their work and Squad cannot override that. If Squad were to prohibit a mod being distributed in accordance with the CC-BY-SA 4.0 then such a mod simply cannot be distributed at all. (Unless either Squad or the original artist budges and offers new terms, of course.)*Actually it's not Squad at all, it's DEPORTED B.V. but that's another story. The same may apply to gameplay videos, it depends on whether they're considered "Adapted Material", whether they might fall under fair use, and so on. Older CC licenses explicitly refer to the right to "publicly perform" which I would think includes playing a game that features the material.