This is either an extremely weird timing coincidence... Or someone saw the announcement/devlog of Plasma Studio and decided to vibe-code-front-run it as a paid offering. This page appeared 3 weeks ago.
Original video a month ago for the plasma studio which is basically the same thing: https://youtu.be/WlgrCqgnk-M
Devlog #1 https://youtu.be/JDsoKhgNtHQ
More design / timelines https://youtu.be/L1O2ALT0A14
Likely just a coincidence. There is a huge number of node-based image editors: https://www.google.com/search?q=node-based+image+editor&udm=...
Is there more of a smoking gun than its a node based editor?
Most of the game industry tooling is supporting that these days. Unreal, and Unity but also Houdini, Blender, Maya...
Node-based editors are not new.
The Arc homepage is clearly vibe slop but with 75 nodes and backend supposedly coded in C, it looks to me like it would have taken a couple of months to get here at least, certainly not a release within 1 week of Youtube-person's mention.
It doesn't seem to be open source unfortunately.