The pink stuff certainly won't hurt your water heater, but it still would take at least 6 or 7 gallons to pump through the lines and fill the W/H. The water heater had to be FULL in order for your downstream hot water pipes to get any antifreeze in them.
What I'm saying is if you only drained 1/2 gallon out of the W/H, then you have hot water lines that never got any antifreeze in them
The W/H bypass is just so you can drain the W/H completely and still fill the water lines, saving gallons and gallons of expensive pink stuff.