Why would the single largest anti communist force on the planet back communists?

To address this comment in the linked thread - The US backs literally everyone all the time.

That might seem contradictory, it isnt, the US backed Castro during the Cuban revolution by sending them material aid and money. Does that make Castro compromised by the US? Of course not, like Marx said when talking about trading stocks; it is good to deprive the enemy of its money.

Thats just how rich the US is, it can afford to hedge its bets by funding literally every side of a conflict so if one wins it can leverage this support, of course it will make its primary motives clear in who it most funds but it will usually use indirect vectors to also hedge on the unfavorable odds, usually through proxies; this is most apparent in how they initially supported the Khemer Rouge by creating the conditions that allowed Pol Pot to take power and using them as a Balwark against China/Vietnam/Laos.