They didn’t do anything that would cause damage to the head gasket.
It’s also possible (and probably fairly likely) that the gasket was not showing any signs of damage externally before it blew.
The head gasket is between the cylinder head and the engine block. This picture shows you where the head gasket is relative to the engine. There isn’t much of the head gasket visible from the outside of the engine.
Head gaskets can fail in different ways. They can fail and leave a hole from the cylinder to the outside of the engine, which you can very easily see from the outside of the engine. In this type of failure, you might see something around the area where it is starting to fail just before it goes, but depending on where the failure is located it might not be easy to see. The gasket can also fail internally, between the cylinder and an oil channel or between the cylinder and a water/coolant channel, for example. Not only would you not see anything prior to the failure from outside the engine, you likely wouldn’t see anything from the outside of the engine even after the failure.
Since the roadside report was “Suspect head gasket failure and water pump” that tells me that there weren’t visible signs of the head gasket blowing from the outside of the engine, which means that the gasket most likely failed internally.