I‘m wondering what I should know about motorcycles. He is going to teach me and I‘m going to go to school but im just so thrilled! It‘s a Honda Shadow 600cc.
Assuming you can get and afford the insurance a 600 for a starter bike is the last thing you want to be learning on so buy a cheapo 125 and keep t'other one for when you can actually ride. All of this is assuming you have a big bank balance to afford the insurance on a 600!!!
I would say if you put less than a quart in the radiator then forget it. If you put in a gallon or more, flush it. In between, flip a coin. What is worth more, the cost of a radiator or the cost of new anti-freeze.
I would flush the cooling system just to be safe. The window fluid may not cause any problem at all but why take that chance.
Take the safety class, it's taught by teachers that ride, not riders who can't teach. Anything else is a Crash Course.