Apparently one of their coolants is not compatable with some other types of coolants and has a reaction to the mix.
Purple G12 Plus is compatible with the red G12 coolant additive. Engine coolant G12 Plus must not be mixed with other coolant anti-freeze. Mixing with other coolants can cause serious engine damage.
Models: AllNew antifreeze, Part No: G 012 A8F A4: Color = PurpleReplaces Part No: ZVW 237 G12 (Pink)Can be mixed with ZVW 237 G12 (Pink)DO NOT mix with ZVW 237 105 (green) or any aftermarket antifreezeDOES NOT replace Part No: ZVW 237 105 (green)Antifreeze, Part No: ZVW 237 G12: Color = PinkCan be mixed with G 012 A8F A4 (purple)DO NOT mix with ZVW 237 105 (green) or any aftermarket antifreezeDOES NOT replace Part No: ZVW 237 105 (green)Regular antifreeze, Part No: ZVW 237 105: Color = GreenDOES NOT replace and cannot be mixed with Part No: G 012 A8F A4 (purple)DOES NOT replace and cannot be mixed with Part No: ZVW 237 G12 (Pink)Follow coolant mixing instructions Cooling system - Service and Repair - Procedures - Draining and Filling , for the Model you are working on.
I might sill get a second opinion on just how much damage has been done to the engine. If you know that you severely overheated the engine, then it may be possible to have that much damage but if you didn't, get another opinion on it. You'll need to at least flush out the coolant and refill with the correct fluid before attempting to drive it if it's still drivable.