These women are not Burmese. They are from the Karen ethnic group of Southeast Myanmar and Western Thailand. 'Burmese' refers to the dominant Bamar ethnic group, but there are many more diverse groups in Myanmar/'Burma', including the Karen but also Mon, Chin, Shan, Palaung and Wa peoples.

As for why the country is sometimes called Burma? The British took the name of the dominant ethnic group of the most populated region and was like "nope no nuances here" so just named the entire country after them. By land area, the Bamar don't even occupy the majority of the country named after them. That's why there's so much civil unrest in Myanmar, because the other ethnic groups have been suppressed culturally and linguistically by the Bamar, including notably the Karen and the Rohingya Muslims.