I tried looking for what made the LLM generate a command to wipe the guy's D drive, but the space problem seems to be what the LLM concluded so that's basically meaningless. The guy is asking leading questions so of course the LLM is going to find some kind of fault, whether it's correct or not, the LLM wants to be rewarded for complying with the user's prompt.
Without the transcription of the actual delete event (rather than an LLM recapping its own output) we'll probably never know for sure what step made the LLM purge the guy's files.
Looking at the comments and prompts, it looks like running "npm start dev" was too complicated a step for him. With that little command line experience, a catastrophic failure like this was inevitable, but I'm surprised how far he got with his vibe coded app before it all collapsed.