The blog post indicates the opposite. The geometry problem in the IMO problem set was solved by AlphaGeometry 2, which is an LLM based on Google's Gemini. LLMs are considered relatively general systems. But the other three solved problems were proved by AlphaProof, which is a narrow RL system that is literally based on AlphaZero, the Go and Chess AI. Only its initial (bootstrapping) human training data (proofs) were formalized and augmented by an LLM (Gemini).