They said that he was a “useful idiot” which has a specific meaning.
https://en.wikipedia.org/wiki/Useful_idiot
A useful idiot is a person perceived as propagandizing for a cause—particularly a bad cause originating from a devious, ruthless source—without fully comprehending the cause's goals, and who is cynically being used by the cause's leaders.
I notice that this post currently has three downvotes.
Whoever downvoted a video of a cute bunny posted to c/aww is probably in the wrong place.