<< Sources please for that claim.
The source is myself. I helped several hundred of the boat people to resettle after they arrived here in the late 70s and early 80s and were helped by a number of church groups. I was initially very surprised at how many did not speak Vietnamese. I had expected to be able to talk with them, since I was an interpreter when I was in Vietnam. Even my Vietnamese wife who has been a citizen since 1972 could not converse with them.
And that’s my source.
Your experience is anecdotal and cannot be said to represent most of all the refugees from Vietnam, even when it is true that many were ethnically Chinese - it makes no difference. Most of the Chinese in Vietnam were Vietnamese citizens, of ethnic Chinese origins, with families who had been part of Vietnam for generations - just like the Chinese of any Chinatown in the U.S. If there were “refugees” from the U.S. (for some unimaginable reason) would you classify Japanese Americans as not really “American refugees”?