To generalize

In technical terms there are no differences, both communities (including Manjaro, and other arch-based communities) collaborate with each other (finding/fixing bugs, documentation, etc.). The key differences are in the social/political field. The parabola project is more concerned about social aspects of technology and its impact in all the spheres of human being: freedom/free will, planned obsolescence, social movements, environmental issues, morality/ethics, etc. In contrast the Arch project is more concerned about the technological aspects: the limits of computing and technology in general (less political).

The same happens with Trisquel/Debian, FSF/OSI, etc.