@Aatube I don’t see how OP is making it a big deal. That post is merely stating facts, as confirmed by the company representative in the GitHub discussion. Yes, the project was never “open-source-like governed”, but it was technically open-source software. With the additional restriction in the license it’s not anymore. All pretty theorical, but nevertheless true.
Up until a year ago, the README explicitly said they didn’t claim to be an open source project: https://github.com/jgraph/drawio/commit/8906f90ac0cc50a0c6da77c28cf9b2b2339277b1#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5L10