I don't completely disagree with your hypotheses but it feels like the hard part of his TIN stuff isn't BM25 (which has been around for donkeys years) it's all the hardcore storage engine work around it. And is an LLM particularly good at e.g. segment merging under a thousand updates a second? I've had a few situations where I've been told "we've hit the perf floor" by Claude only to have persisted myself and shaved substantial amounts off still.
More damning for the theory might be that I think paradedb's pg_search predates the agentic coding by a few years?
ParadeDB/pg_search developer here. Yes, we started the project before LLMs. Moreover, our project is now much more than just full-text search.
I do agree with the sentiment here that many of the other FTS-in-Postgres projects in recent years have been heavily enabled by vibe coding.