Freehub silent after service

The only damage grease could do in the pawls is that the freehub doesn't work. If your ride home went okay, I assume the freehub works at whatever temperature you did the ride in.

However, I find it hard to visualize how the freehub could have been greased. Opening the freehub body is not an easy task, if it's a Shimano freehub.

If they really greased the freehub body inside, given that it worked in your ride temperature, the only bad effect could be that it no longer works in freezing sub-zero-Celsius temperatures.

As a matter of fact, Shimano freehub bodies come from the factory with a grease that is not perfect in freezing sub-zero-Celsius temperatures. It barely works, but only barely.

More likely is that they oiled the freehub body, because unlike greasing which would require a full disassembly, oiling is possible without full disassembly.

Oil will do no harm even in freezing sub-zero-Celsius temperatures... unless it's a very very thick oil indeed.

Why won't you ask the shop what they did to the freehub body and ask for an explanation for it being quiet? Presumably as a reputable shop they remember what they did, and can tell you the exact weight of the oil they put into the freehub body, from which it can be estimated whether or not it works well in freezing sub-zero-Celsius temperatures if you choose to ride in such temperatures.

Besides, if the freehub is Shimano in well-lubricated condition it should be very quiet. You can hear it in quiet indoors environment. When riding the bike outdoors, it is barely audible. If there's any traffic noise you won't hear it.