1995 Ford Taurus water pump

I just installed a new water pump on my car. But I didn't do step one. Drain the radiator. I believe I got everything else right. One other thing tho. I drove it maybe 350 yards with very very very low oil I pulled it over and the engine was smoking. So I put oil in and drove it about 5 miles as I was driving I heard knocking in the engine. After 5 miles the engine shut off. I can drive the car but only at low speeds and it eventually over heats and shuts down.

my question is did I mess up the piston with driving it with no oil? Or is it that I didn't drain the radiator before replacing the water pump. I was told there could be air pressure built up in the lines not allowing the water to circulate. The knocking sounds like a baring in a spray paint can but not a random noise the knocking is on time only changing slightly and recuring in rythem.