What definition of "vibe coding" are you using here? I seriously doubt Claude Code was made "mostly" (or even "partly") by telling a prompt what they want, and accepting the output when it looks functionally acceptable without regard to how the code looks or works under the hood.
I don't know if or how you've been using AI for coding, but Claude Code is almost certainly being used to develop itself, and I have a hard time imagining their devs not having the best setup possible to make it as easy as possible for Claude Code to iterate on itself with minimal oversight. Once a codebase is well structured and you supply a well thought out meta prompt with something like CLAUDE.md, then there's no reason to check the code output/changes beyond a quick skim.
What definition of "vibe coding" are you using here? I seriously doubt Claude Code was made "mostly" (or even "partly") by telling a prompt what they want, and accepting the output when it looks functionally acceptable without regard to how the code looks or works under the hood.
... Which is what "vibecoding" is.
Vibecoding != AI assisted/agentic coding