That explanation is right. It's the move from the five-year to the 10-year passport. As more Canadians move to a 10-year passport, and the $25 fee is only charged at the time of obtaining the passport, that creates that large dip in revenues. You see in the chart, as well, that afterwards the revenues will start to go back up again.
On June 5th, 2018. See this statement in context.