For everyday Indonesian citizens? Probably just the fact that Hanoi/Ha Noi is the capital city and Phở is the most famous dish.
I had the privilege to study overseas and met and hung out with some Vietnamese. I also went to the country to visit them. I learned that:
They spell Vietnam as Viet Nam.
Vietnam was colonised by France.
There is such thing as “High School for the Gifted”.
Vietnamese has six tones.
Vietnamese name can be pretty long.
Vietnam is also famous for its coffee. And egg coffee.
Vietnamese people also celebrate the Lunar New Year (Tết). Before meeting them, I thought only mainland Chinese and the Chinese people around the world celebrated it.
Water puppetry is quite nice.
There are also pedicabs in Vietnam, though I think they are more for tourism purposes as opposed to Indonesia, where they are still used for transportation.
Obama made a bún chả restaurant in Hanoi famous.
Northern Vietnam has four seasons. Southern Vietnam has two seasons.
Hồ Chí Minh was a person.
Scooters/motorcycles in Vietnam do not use rear view mirrors. The helmets used there are what the Indonesian people consider below standard.
Dogs can be food.
Vietnamese drive on the right side.
Crossing streets there is an… experience.
Vietnamese Dong is weaker than Indonesian Rupiah
LGBTQ is not punishable by law there.
And many others that I can’t think of right now ????
All in all, it comes down to each person, whether or not they are willing to learn about other cultures when they have the means to.
The majority of Indonesian people do not have the chance to meet Vietnamese people and there is very, very little information about the Vietnamese culture available in Indonesia. I would not have had the initiative to learn about Vietnam had I not met my friends during my study overseas.