Yes, that's correct. They have become a lot more strict on this.
It was always the intention that the multi-partner reward chart was intended to allow the use of Avios for redemptions on partner airlines for trips that couldn't easily be served by BA. In the terms and conditions you will see it says they can be redeemed via the most direct routing for a one way or roundtrip.
If you can find where it says up to three stopovers are allowed that would be very interesting.
I suspect that the stopover in HKG is making it 'not most direct routing' so it's now not a one way trip or a roundtrip, but three journeys. If you drop it I suspect it will be fine. Your open jaw at the end is MNL-HKG which they could push back on since you are backtracking to HKG, but let's hope not eh?