First of all, that was mentioned in a very specific context, when I was comparing Thailand to Malaysia, saying that Malaysia hosts a lot people from China, India and other countries, while in Thailand the majority are Thai people. I even mentioned that closer to the borders country gets more diverse.
Secondly, there are approximately 70, not 30 ethnic groups in Thailand. But ethnic groups and nations are different things. For example, in Germany you can also find different ethnic groups but overall these people are presented as Germans. You can find ethnic diversity everywhere. But having people of a different nationality means having people with relatives abroad that speak different language or confess other religions or … you can continue the list.
Anyway, I clearly did not want to sound offensive and I am sorry that you felt this way while reading my post.