It was a bugfix first, balance change as a result. They can be both. A lot of what we use for guidance is how the client is constructed, but we have to also take into consideration that Mythic didn't have everything correct or logical by the end of live either. This wasn't a remotely controversial change as the client appeared correct, and the Bright Wizard using a very similar tactic was setup correctly as reference.
Evaluating bug reports will certainly continue into the future and skills will be changed on a case by case basis to the best of our ability using the same logical conclusions and inferred information from similar skills. If we want to make a clear balance change, those will come as a result of larger and less frequent patching. Now in the next couple of years if someone decides to do frequent balance patching directly counter to what I've said, and the playerbase decides to quote me as a gotcha, I will defer to the better judgement of the current devs.