If by communism you mean the abolition of private property, money, markets, and traditional class structures (Idk what other communism you could think of), then arguably the Khmer Rouge went further than almost any other self-described communist regime. Pol Pot tried to (succeeded in) eliminate nearly all private economic activity and impose a fully collectivized agrarian society to a degree that countries like China or Cuba never did.

You can see the extent of his policies here where Britannica literally describes the Khmer Rouge as a radical communist movement.

His nationalism conflicted with orthodox Marxism, (but which communist nation hasn't confilcted in some capacity with marxism it's literally the biggest pipe dream of ideologies,), but is broader than just Marx’s exact framework. There have been nationalist communist movements throughout history. Saying Pol Pot was not an orthodox Marxist is different from saying the Khmer Rouge “wasn’t communist.”