My guess is: The SinoPharm vaccine is protecting pretty well against serious disease and death, but it's not as effective against Covid19 spreading in your body.
The exciting question is: How likely is it that (SinoPharm)-vaccinated people can spread the virus?
The issue with every vaccine: No vaccine in the world can protect your body from getting infected with the virus. What a vaccine does is to train your immune system to quickly fight the virus so that the virus cannot cause disease.
My assumption (which I cannot prove so far) is that the mRNA-based vaccines (e.g. BioNTech, Moderna, Curevac) are more effective in training the immune system to quickly kill the virus -> so that a fully-vaccinated person is much less likely to be able to spread the virus.