My guess is that Canada is careful about selecting those allowed to migrate for education which helps a lot here.
That said, the opposite is true for refugees. The only thing you need is to somehow get inside the country. If you can convince some judge that you have a moderately believable story about why you will be in danger if you go back to your country you can get refugee status.
So there's basically two classes of immigrants. Those that are selected with very high standards, and those who just get in with almost no standards.
I'm guessing the latter group does not even send their kids to Universities.
Immigrants also have to restart from scratch. Everything in Canada is completely different from what we're used to in our countries of origin. Often, parents who were engineers in their home countries have to work blue collar jobs to make ends meet.
I think the actual difference is in average IQ and other desirable traits like industriousness.
Immigrants tend to be at the higher end while refugees tend to be at the lower end.
Why would people fleeing war zones be on average less industrious or less intelligent? That doesn't make any sense.
However, being a refugee means going through a much more traumatic process than being an immigrant. You are literally thrown from your home with little left and have gone through a difficult process to get out and resettled in a new country. So drug abuse, gang activity, crime, not doing well in school, depression, etc...were problems for that community even though given normal circumstances they would have been similar to other Chinese immigrants.
I'm not sure about your explanation though. Chinese people are not magical people. IQ is still distributed on a bell curve in China as well. If a chunk of people from a country exhibit characteristics that indicate they might be on the lower end of the bell curve, they might just be on the lower end.
The Boat People had traumatic experiences, so why wouldn't you expect them to have issues when arriving in their new host country? War, rape, murder, starvation, that shit will screw with your head for maybe the rest of your life. There is no point in comparing refugee and non-refugee immigrant experiences.
Ethnic Chinese were successful in Vietnam, just like the rest of southeast asia, many of them were rich, college educated and so on, and still got messed up for a generation upon being kicked out during the Sino Vietnam war. We aren't talking about soso people who weren't successful in their previous countries. Heck, today, many of the refugees that make it to the west were relatively successful, or they simply wouldn't have had the resources to make it to the west.
People are not all equally intelligent or hard working.
This is very different from US where you have a green card lottery and your typical immigrant is just an average population because everyone has the same chance of winning lottery, it doesn't matter if you are a farmer or aircraft engineer.
The refugee system in Canada is frequently abused. I hear anecdotes from my friends about kids from rich families in safe Easter European countries, that pay thousands to immigration lawyers and apply for refugee status simply because the partied too much and didn't manage to get enough points to go through the point based system. Such "refugees" can be safely compared with immigrants.