Prediction is an appropriate word to use when you are stating something you believe to be true about something unknown.

'The sun will rise tomorrow' is a pretty weak prediction, but we don't truly know that the sun will rise tomorrow. However, we can be pretty sure it will based on probability, history, likelihood, from our own past observations. You wouldn't need much convincing to believe the prediction.

'The sun will not rise tomorrow' is a much stronger prediction, because it's a 'wilder' less believable claim with very huge impact. Nobody would believe the statement without proof.

A hypothesis, is a testable statement about a predicted outcome. You could hypothesize something like: 'The Earth's core will stop due to XYZ event, which will stop Earth's rotation. The sun will not rise tomorrow.' Then you go about designing experiments (or you observe and show something that is measurable, like some asteroid on a path close to Earth's) to prove the statement.

From the article: 'Charles Darwin posited that some species from the genus Saxifraga—a group of flowering plants typically found in alpine environments—may be carnivorous because of their sticky glandular hairs, which can trap insects'.

'Posited' is to suggest, assume, or put forward an idea, theory, or fact as a foundational basis for an argument or investigation. 'Posited' isn't quite as strong as the word prediction, it's more like a sensible suggestion for further study. Darwin had observed carnivorous behavior in other plants with sticky hairs, and suggested the behavior may be observed in another plant as well.

He didn't make a strong claim like: 'The genus Saxifraga plants are carnivorous because they have sticky hairs that trap insects.' This sort of claim suggests that plants with sticky hairs always trap insects for nutrients, and frankly, he couldn't know that's true without observing every plant with sticky hairs.

What if there are plants with sticky hairs that use the stickiness as a defensive measure instead?

Should the article have used a different word than 'predicted'? Probably, but it wouldn't attract as many viewers, and 'predicted' sort of lends Darwin deserved credibility.