He indeed was no fan of Lenin or communism (as /u/jurijfederov points out), and I think it was an absolutely ridiculous choice to add Lenin to this mural. It's not the place for that, it totally distracts from the issue at hand.
However, I do think we should be careful not to take this too far, ie to mean he was a capitalist. He was in fact quite the anticapitalist. (To preempt accusations of whataboutism, I want to make it clear that I am emphatically not asserting that anyone here has said he was a capitalist, but I just want to situate King's thoughts in the proper context and avoid this devolving from the specific, justified critique of this mural into a generic anti-left circlejerk.) He roundly condemned capitalism as well as well as communism. In a speech to the Southern Christian Leadership he stated that “Capitalism forgets that life is social. And the kingdom of brotherhood is found neither in the thesis of communism nor the antithesis of capitalism, but in a higher synthesis", and in another speech that “The evils of capitalism are as real as the evils of militarism and evils of racism.”
He even saw merit in Marx: "In his 1958 memoir, he reported that although he rejected communism’s central tenets, he was sympathetic to Marx’s critique of capitalism, finding the “gulf between superfluous wealth and abject poverty” that existed in the United States morally wrong (Stride, 94)".
In a letter to Coretta Scott he wrote “I imagine you already know that I am much more socialistic in my economic theory than capitalistic… [Capitalism] started out with a noble and high motive… but like most human systems it fell victim to the very thing it was revolting against. So today capitalism has out-lived its usefulness.”
And his views on racism were intimately connected with his anticapitalism, as can be in a 1967 report to SCLC staff, in which he states that "We must recognize that we can’t solve our problem now until there is a radical redistribution of economic and political power… this means a revolution of values and other things. We must see now that the evils of racism, economic exploitation and militarism are all tied together… you can’t really get rid of one without getting rid of the others… the whole structure of American life must be changed.”
And most plainly stated: "W]e are saying that something is wrong … with capitalism…. There must be better distribution of wealth and maybe America must move toward a democratic socialism.”
Again, the mural was a stupid idea. But the reason it was stupid was specifically not that it draws a(n abstract) connectionn with leftist politics, but because it distracts from the issue at hand in a totally unnecessary way. There was a fantastic opportunity to celebrate the contributions of individuals more directly relevant to the struggles at hand (e.g. other Civil Rights Leaders, present day figures, etc.), but it was unfortunately ruined.