Do you mean that if the US Marine Corps takes some foreign territory by force, it's not an invasion, because there is no army involved in the operation?
Vague everyday language is unsuitable for contracts. When there are multiple reasonable interpretations, it's impossible to know what has been agreed. It's better to be pedantic and use precise language and narrow technical definitions of words.
In some languages and situations, "army" is a general term for the military or for a military force. In other languages and situations, it refers specifically to ground forces. Americans are usually in the latter camp, especially if they have a connection to the military.
I meant that the person writing the contract must be a pedant. Vague everyday language can only lead to bad things, when someone inevitably interprets in a different way.
In this particular case, the bets were clearly about military operations with the intention to take control of Venezuelan territory. This is the established meaning of "invasion", in contexts where people care about distinguishing between different types of military operations. But because people could plausibly interpret the word in a different way, the rules did not use words "invade" or "invasion" at all.
Vague everyday language is unsuitable for contracts. When there are multiple reasonable interpretations, it's impossible to know what has been agreed. It's better to be pedantic and use precise language and narrow technical definitions of words.