You should check again because it is. Your mistake is trying to apply an economics definition to a national security issue. It simply does not apply. There is no criminal statute that defines collusion, it would be conspiracy to defraud the United States, conspiracy to violate campaign finance statutes, etc. So if we are talking about legal definitions we shouldn’t even be saying ‘collusion’ at all. We should be talking about specific criminal statutes.
If we are using collusion in the colloquial sense then, as we should be, secretly meeting with representatives of the Russian government in order for them to contribute dirt on your political opponent would be obvious collusion.