There's certainly a fuzzy line there somewhere, but the Maduro raid is clearly on the non-invasion side of it. This operation was much more similar to the Bin Laden raid than to even the smallest operation that could be considered an invasion.
Intent is important here. It’s an invasion if the objective is to establish sustained military control over some portion of the country’s territory.
But if the intention is some other military objective: blow up a military base, kidnap a president, etc, and get out quickly, then I don’t think the word “invasion” applies.
I have no idea who has decided that "invade" means "establish sustained military control".
With certainty that is not the original meaning of the word. In Latin and in classic English, the meaning of the word is just: "enter in a hostile manner", as it can be verified in any dictionary.
As long as foreigners have entered the territory of another country by force, that is an invasion.
It does not matter which was the duration of the invasion or whether the intent of the invasion was to stay there permanently.
An invasion may be followed, or not, by a military occupation, which is "establish sustained military control".
The real answer is that the people that set up the bet decided, and they listed the conditions upfront.
And imagine how silly it would be if 1-5 soldiers came across the border by force and left a few minutes later and that counted as a major world event!
Compared to other dictionaries, this is a very poor explanation of the word.
Nevertheless, even here it says clearly that "invade" refers only to "enter", and neither to "subjugate" or to "occupy".
Other dictionaries explain better the distinction between "invading" and normal "entering", which is in the manner how one enters, i.e. "in a hostile manner" or "by the use of force".
Your dictionary explains the distinction by intent, not by manner, but this is wrong, as at the time of the invasion one cannot know which is the intent, which will become known only in the future.
By this definition one could never recognize an invasion while it happens, even when one sees a foreign army entering and killing everyone on sight.
I agree however, that the Polymarket bet has specified that the object of the bet was an invasion followed by an occupation of the territory, so the conditions of the bet have not been met.
How slowly would it need to be done to be counted as an invasion? A day? A month?