There is no exact definition but BERT would probably just be a LM, not a "large" LM.

Is the exact definition important? The point is, they developed a thing and integrated into their core product. BERT allows them to handle conversational queries much better than before.

I think it does, because LLMs allow things that LMs like BERT don't - like answering complex question on their own etc which is being discussed in the context of this thread.