The Governor General did what the Prime Minister asked her to do, which is what they always do. The GG does not act on the advice of parliament but rather on the advice of the Prime Minister.
If you presented an example where the Prime Minister told the Governor General to do one thing, and she did another, then I'd agree that counts as the Queen/GG exercising power.
The article I linked lists two such examples. More importantly, my point was that in this case, although the GG chose to do as asked, that was by no means a set outcome. If she had done otherwise, as happened in 1896 and 1926, that outcome would also have been considered reasonable, and most likely not resulted in a public outcry and overthrowing the monarchy.
I still think it was a bad call allowing Harper to get away with prorouging parliament twice and giving the cons time to paint a coalition government as somehow "unconstitutional" and "undemocratic".
If you presented an example where the Prime Minister told the Governor General to do one thing, and she did another, then I'd agree that counts as the Queen/GG exercising power.