Sentiment analysis on text predates LLMs by quite a bit, and it's not exactly a secret that pretty much all of the major LLM products have been tuned to take into account inferences about how the user is feeling (e.g. the sycophancy being dialed up to the extreme, whether that's because it makes the products more sticky or to avoid stuff like the "I have been a good Bing" fiasco from from a few years ago