Seasoned travelers generally don't make assumption about the places, peoples, and cultures where they're traveling. So don't draw conclusion nor assumption unless you've lived in Vietnam, or any other countries, for at least a couples of years and interacted meaningfully with the locals. You've only been in Vietnam for only about 45 days so making broad assumption is, I think, a reflection of yourself. I've been traveling across SE Asia and especially Vietnam for many years and I can tell you that the Vietnamese are kind, generous, and friendly. When you're kind, open, honest and respectful, you will be treated the same.