Is this perhaps some weird British vs American English thing I was unaware of?

Oxford Learners Dictionary (because the Oxford English Dictionary is behind a paywall): "a statement that says what you think will happen; the act of making such a statement" https://www.oxfordlearnersdictionaries.com/us/definition/eng...

The current Wikipedia definition looks like a good fit for how I'm using the term here:

A prediction (Latin præ-, "before," and dictum, "something said"[1]) or forecast is a statement about a future event or about future data. Predictions are often, but not always, based upon experience or knowledge of forecasters. There is no universal agreement about the exact difference between "prediction" and "estimation"; different authors and disciplines ascribe different connotations. https://en.wikipedia.org/wiki/Prediction

No, it's just a matter of not trying to make "guessing" equal to "predicting". In this day and age we should know better then to make wild guesses.