It's another good question.
We have another provision in the code in that similar type of language, “engaged in the performance of their duties” and it has been interpreted fairly restrictively in those contexts as relating to a specific duty that the professional has and that they are engaged in performing that duty, just as the words would say.
I think it's an open question as to whether the courts would interpret this provision as encompassing the bus driver who is perhaps inspecting the vehicle before they start driving it and is assaulted at that moment, for example. The wording doesn't preclude it, but it wouldn't surprise me that it is something that would be subject to litigation to determine what the boundaries would be.