That red cow is on Vietnamese restaurants all over North America and possibly further, but I've never seen one anywhere else I've traveled.
I don't think they all just decided to adopt it because it was cute, copyright be damned. Also, the images are not identical to La Vache Qui Rit
I don't know the specifics to the Vietnamese, but a red cow has religious significance in Judaism. It may be a similar situation here.
A cursory check on the internet of Vietnamese cultural information shows that the country is comprised of many religious and cultural groups, including Hindus who hold cows as sacred.
Of course, they serve beef in these restaurants, which doesn't really match with that, so who knows!