At first I doubted if it's "Hmong" in Sangklaburi until I read more. Yes you are right. Hmong and Mon are different ethnic groups. Hmong is, as you might know, hill tribe yet Mon is a lowland people. Their cultures, languages, etc. are all different. Note here since many don't know much about Mon. They are very close to Thai and has lots of influenced both in culture, history, and scientific way. They established one of the earliest kingdom is SE Asian Dvaravati (Google if needed) which founded since 6th century, even before Khmer Empire, yet the world hardly know them because their historical sites are not as marvelous as the latter. DNA study also show that most Thai in every regions are mixed with Mon except for the north which is the fewest of all.