If Canada is trying to mirror what the US policy is, the US policy clearly states that transit passengers (< 24hrs) passing through HKG would not require a covid test:

https://www.cdc.gov/coronavirus/2019...travelers.html

But you are right, the Canada Immigration page does not clearly distinguish this. I can only presume that they will likely clarify this to mirror the US in the coming days (hopefully). We are in the same boat for a BKK-YVR (connecting via HKG) trip in April and trying to decide if we should change our flights now.