The post takes real legal uncertainty and cranks it up to maximum alarm. The actual state of things is more nuanced and still evolving — courts are working through these questions case by case, and the Copyright Office indicated that a future may arise in which prompts could "sufficiently control expressive elements in AI-generated outputs to reflect human authorship."
So it's worth being thoughtful about this stuff, but "your vibe-coded repo is public domain" is not an accurate summary of the law.