Because it was trained on news sources that say "Over 80 fatalities in tornado outbreak"?

I can't say I'm sure, you'd have to know the training data involved, but it is quite common for mass casualty events to have "more than" or "at least" in their subjects along with multiple articles where the count increases over time. Remember and LLM is not wikipedia. If it has confidence of a more exact answer it will most likely give you that, but it's not guaranteed.