What really reinforced this for me was that I recently vibe coded a home assistant addon that, as it turns out, there was a github project that did almost the same thing. The initial implementation that came out of the LLM was essentially the same just with just some small tell in things like the logging that came from what I prompted it.
It was a very small project (maybe 500 LOC) so there's a greater chance of coincidence but it really felt like the office junior had just ripped off someone else's work and tried to hide it (badly) and really, that's exactly what they do