In general, it is not common for Vietnamese people to get offended when Tet is referred to as Chinese New Year. Vietnamese Tet, also known as Lunar New Year, shares some similarities with the Chinese New Year, as both are based on the lunar calendar and involve similar traditions. However, there are also cultural and regional differences between the two celebrations.
While some Vietnamese people may prefer the term "Tet" to be used to specifically refer to the Vietnamese New Year, the majority of Vietnamese individuals understand the connection between Tet and Chinese New Year. They recognize the cultural exchange and historical influences between Vietnam and China.
It's important to note that individuals' reactions may vary, and there may be some who are more sensitive to the distinction. To show respect and avoid any potential misunderstandings, it is always a good practice to use the term "Tet" when specifically referring to the Vietnamese New Year in Vietnam. However, if you are discussing the general concept of lunar-based New Year celebrations, mentioning the connection to Chinese New Year is usually well understood and accepted.