2 days trip from Hong Kong to Guangzhou.

If you fly from HK to Guangzhou and then back to HK, you can enjoy this policy. However, if you fly from HK to Guangzhou and then from there take a flight back home or to a third country or region, you can get the 72-hour free transit stamp.

I think what it means is if you fly hk - guangzhou - hk, you cannot use this policy since that doesn't count as transit. You can try hk - guangzhou - bangkok - hk, then you can use this policy, but that means you have to fly additionally to Bangkok and back, too bad there is no guangzhou macau flights...