Could someone give me sources that state early Lao did not come from southwestern China (southwestern Chinese province of Yunnan)?

my father once told me that we occupied parts of soutern china.. so i guess we were from china.

Yep, we Lao people all once dwelled in Southern China until we migrated South and settled in the Mekong valley.

A lot of Linguists have speculated that all the Tai (Lao included) people originated from the area around Muang Theng (Dien Bienphu) because of the diversity of Tai dialects being centered around this area which are very close in proximity to one another, i.e. Tai Khao, Tai Dam, Tai Dam, Tai Lue, Phu Tai; and they moved to all directions to form their own group names and separate dialects. This is only speculation from some linguists.

We came into the region just as the Khmers were dwindling.