tbf, whilst the Viet Cong were often nasty to their civilians, the Khmer Rouge killed a quarter of their own population and had made multiple advances into Vietnam to continue a genocide that had started with ethnic Vietnamese living within Cambodia. It's not really a tenable argument the Viet Cong didn't have just cause for invasion or that their military sticking around whilst the remaining Khmer Rouge cadres waited for an opportunity to return resembled Western colonialism, and the Khmer Rouge is not fondly remembered by Cambodian nationalists or royalists or anticommunists
Hun Sen, the Cambodian they installed as deputy PM is still in power having allied with just about every faction in Cambodian politics in various elections and coups; not a testament to the vibrancy of Cambodian democracy but a testament to how the real distinction wasn't between an independent Cambodia and occupation, but between the Khmer Rouge and everything else.