An important part of the article:

"The consensus in Hanoi is that Beijing is the nation’s primary external security threat. China has a long history of imperialism in Vietnam and invaded the country as recently as 1979 in support of the Pol Pot regime in Cambodia, resulting in a brief war in which roughly 70,000 people died. Although relations have improved since the 1990s, Vietnam remains highly wary of its much larger neighbor despite sharing communist rule."

There is a lot of distrust of China throughout Asia. Huawei is having an easier time selling to Western countries than to China's neighbors.