It depends on whether they did a drain and refill of the radiator or performed a flush of the system.

There are two likely possibilities:

1. They simply drained the roughly 2 gallons of coolant that comes out when you open the radiator petcock and added back your 2 gallons of 50/50 premixed coolant. You should still have 50/50 mixure. You would also have approximately one gallon of older coolant that is still in the system because the engine block was not flushed or drained. The fluids are compatible and the resultant color would be blue once mixed.

2. They drained the radiator and then continued by flushing the system, to include the engine, with water. The coolant that was in the engine is now replaced with water. They added your two gallons of 50/50 mix to refill the coolant system. You now have roughly a 33/67 mixture of coolant/water.

The correct premix ratio when flushing the system is 75/25 coolant/water unless the engine block is also drained.