Based on what I could find, it seems that a lot of Vietnamese people went wherever there was better sponsorships since a bunch of people were fleeing the Vietnam War. California and Texas happened to have better conditions such as existing Vietnamese communities, better safety nets, etc.
New York's Vietnamese immigrants in my experience were largely ethnically Chinese and likely don't identify as Vietnamese. Growing up, I knew several families like this. The only real distinguishing factor was that their Chinese surnames were spelled according to the Vietnamese way (Tran for Chen/Chan, Luu for Liu, Phung for Fung/Feng, Ly for Li/Lee). Otherwise they considered themselves part of the Chinese population.