Literally, you're right - in Latin it means "not following". But in conventional usage, non-sequitur is more for things that are so completely out of place for the conversation.

Not a non-sequitur: "Okay, so based on this finding, [insert something topical but wrong]".

Non-sequitur: "Okay, so that's great, but Michigan beating Ohio State means this is irrelevant".

(edit because I did not realize the formatting I used for my non-sequitur example caused it not to render)

Your definition for non-sequitur is correct, however the conclusion that Predators are failing to come of age is a logical conclusion of the stated premise. The actual issue, which you pointed out, is that of using a false or faulty premise (that all Predators in the movies are on their first hunts). The validity of an argument isn’t a function of how true a premise is. So you were right that op was wrong in their conclusions, you just mislabeled the issue

It's all about the same movie series canon, none of this is non-sequitur. They would have to be talking about Predator canon and then just start talking about Terminator or something. And even that's not a great example, because Arnold is in both of them.

A non-sequitur would be walking 5 feet across the floor and finding yourself in a jungle somewhere. In a place not connected to the place you just came from.