Customer good will? Just what did the shop do wrong?

In general changing tires isn't a reason to realign even if the tire diameter changes on all 4 wheels by the same amount. If the front to rear diameter changes dramatically, the caster angle will change. On large trucks the frame angle is measured and input to a chart to determine the correct caster angle to be used.

Now, if the old tires had camber wear and the alignment was altered to compensate for drift / pull, tire with flat tread may cause the car to drift. This isn't the fault of the shop and is why some shops refuse to align cars with unevenly worn tires.