Not quite so, it is because of an oligarch kid in the kindergarten called "Thailand Elite" named Thaksin misbehaved and thought to be mightier than the mighty. After getting overrun by the political bus 19 years ago he continued to throw his own sister and six weeks ago his youngest daughter under the same bus.
On the other side of the play pen there is another geek called Hun Sen who parked his three sons befittingly in key positions within the Cambodian government. He never managed to rename the country into Hunland, likewise Thaksinland never materialized.
These two individual persons, their ego, their corrupt mind and endless greed for power and money are directly responsible for this absolutely avoidable mess which will leave scars in the economies of both countries and will take generation(s) to heal the hatred and rift between these two people who are so similar to each other.
The Khmer temples, from Western Thailand across both sides of the Dongrek mountain chain to the morning temple of Wat Phu in Southern Laos' province of Champasak are Khmer, not Cambodian, not Laotian and not Thai. All these political definitions of country names today were nowhere a few hundred years ago, lest a thousand years ago when those temples were built!