Prices move because expectations change. New information forces the market to re-price something — and how much it moves depends on how surprising that information actually was.
Surprise matters more than the news itself
If a piece of news is exactly what everyone already expected, it can move a price very little — it was already "priced in." A smaller, more surprising piece of news can move a price far more than a bigger, fully anticipated one.
Overreaction and underreaction both happen
Markets aren't perfectly rational responders. Sometimes a headline triggers a bigger move than the underlying substance justifies, and it partially reverses later. Sometimes real, important information gets underreacted to at first and the price keeps drifting as more people notice. Neither pattern is guaranteed or predictable in advance.
This is exactly what the sentiment component tries to capture
precandle64's news-sentiment scoring is an attempt to quantify this reaction as it's happening — which is also exactly why it's a component of the signal, weighted alongside momentum, rather than the whole story on its own.