As you know, the US has been trying to upgrade relations with Vietnam, to counter China's influence in the region. In response, China has been increasing its support for Cambodia, to offset Vietnam.
In case you don't remember, during the Cold War it was the US and its partner China which supported the genocidal Khmer Rouge in their takeover of Cambodia, to counter Vietnam and contain the rise of Soviet influence client in the region. So basically ultra-murderous Chinese communists ousted the Soviet-supported communists to take over Cambodia. Lacking popular support, the ultra-murderous Chinese communists had to commit genocide in order to maintain an iron rule. This is why a supposedly Cambodian govt decided to kill off its own population. Brzezinski was a key architect of this policy, inviting China to become a partner in this evil game.
Cambodia is so staunchly loyal to China's interests that it refuses to allow Taiwan even a token presence on its soil. Let's watch to see how Phnom Penh behaves towards India.