Ethnic Lao in Cambodia

I remember my mom telling me her male cousin married a lady from Cambodia here in the United States. Then she clarified it by saying she is only Cambodian via nationality but ethnically Lao with a Lao name and everything. My mom says her family lived near the border and just moved further south sometime before the Vietnam War

Now I understands borders are a political thing and the borders were not drawn by natives but rather by foreign colonizers at the time which lead to the creation of these " countries " so it's understandable to have a group on both sides just like Hmong in Laos and China.

I've have seen Youtube videos where they go to the next border city of Strung Treng and shows some small Lao communities and temples. I can't tell if they have been there for generations or they just came within the last 20-30 years.

Does anyone know if there are resources for this information?