2000 Ford Focus wrong liquid in antifreeze holder

Well. It's possible that windshield fluid still does the job as far as cooling your engine, however, it doesn't have the same chemical property as antifreeze. It may not withstand the heat so well, and I doubt it has the same anticorrosion property.
If you flushed the system real good, with a cooling system cleaner, and didn't drive the car while it had windshield fluid, my 2 cents guess is it's not too bad.
I can't garantee anything though.I never heard something like that before.