Buddha was not born in Nepal. Buddha was born in Lumbini, which was part of Kapilvastu Kingdom, Which lies in present day Nepal. Nepal at that time was confined within KTM valley. 

Saying Buddha was born in Nepal, will be equal to saying Dalai Lama was born in China (or Dalai lama is Chinese), because Tibet is part of China. Since Dalai Lama is not Chinese, Buddha was not Nepalese.

Even if you claim Buddha was Nepali, he was not of Pahadi origin, he was madhesi, so you can definitely call him dhoti, like you do while addressing people from Terai.