I think back in January and February, China was dishonest about many things. It appears the local government in Wuhan tried to hide things from Beijing, and likewise China misled the WHO (whether it was because they wanted to save face, or they didn't want external scrutiny, or they were hiding something - I don't know. I'm not interested in political conspiracy theories.). And I'm sure they under-counted back then too.
But I'm only looking at their current daily numbers. They may not be exactly correct but I think they''re within an order of magnitude, i.e. they seem to have it under control currently (though that doesn't mean it won't come back). I'm sure Vietnam has had a few deaths, but whether it's zero or just a handful, they don't seem to have a big outbreak there. They took very early steps at containment. The CDC believes the Vietnamese numbers so I'll defer to them.
Yes, there could be issues with data quality and data sources. But it's also possible that they're just doing a better job at basic public health right now.