Cuba is absolutely a Socialist country. The vast majority of industry is centrally planned by the state. There have been some market reforms to help participate in the global economy after the dissolution of the USSR, but there isn't a Borgeoisie class in power.

This is ideological purity taken beyond rational extremes, if you believe any amount of Capitalism in a country is sufficient to call it Capitalist, then you would disagree with Marx, who advocated for gradually building up the productive forces so that Communism can be meaningfully achieved, and which also requires global Socialism.