Gotcha. Marxists split Socialism and Communism in terms of stages, seeing Socialism as the transitional status where Capital becomes subservient to Humanity, rather than the opposite under Capitalism. The reason Marxists declare that Socialism is transitional is because Marxists believe there is no such thing as a static system, and as such under Socialism Capital will progressively become more collectivized with respect to its development until there is no more Private industry, at which point Communism, ie a fully centrally planned and publicly owned economic system, becomes the next phase.

Communism isn't the end goal, either. With the advent of Communism, there will likely continue to be further evolutions on societal organization, but we can't predict what that will look like without first reaching Communism and observing its trajectories, just like Marx did when noticing Capitalism's tendency to centralize and predicting the Proletariat would sieze it and use the infrastructure for planning created by markets to bring Socialism and eventually Communism into existence. That's where the "Fully Automated Luxury Gay Space Communism" meme/non-meme comes from, as the stage beyond regular Communism.

The other commenter is likely an Anarchist, insinuating that Marxism is Authoritarianism, and therefore not Socialist, though I obviously disagree with that I don't think engaging them directly would benefit anyone right now.

Seriously, the whole definitions of 'socialism' and 'communism' is a context-dependent hell with over a century of baggage. It's hard not to find definition errors in online arguments. In the time of Marx's original writings the two terms were often treated interchangeably as synonyms, while others consider them mutually exclusive stages of development, while other people stretch the word socialism into anything from Bernie Sanders (a supporter of social capitalism and private property, who Marxists wouldn't even consider to be socialist) and I've even seen some odd fellow claiming anything funded by taxes is socialism... a politically useless definition but unfortunately one many people recognise.

Then you get the whole confusion of "-ist" and "-ism". In one context, "communism" can mean a society with a communist mode of production ("money is abolished under communism", "we're trying to achieve communism"), while other times "communism" can mean "the political movement aiming to achieve a society with a communist mode of production", and then the word "communist" can describe a person or group subscribing to that movement. Similar with "socialism"/"socialist". So, common vague questions like "is china socialist?" can be, sincerely, read different ways by different people - they obviously haven't achieved a [fully] socialist mode of production so many will say no (they still ultimately have capitalist economic structures, whether state dominated or not), but they're also evidently a communist state and therefore also a socialist state since it's run by a Communist Party that believes in and attempts a transition towards a socialist mode of production, so many will say yes (in the same way that I call myself a socialist, they call the state of China socialist - neither exists in a socialist mode of production but both subscribe to a socialist school of thought).

When you begin to see the different schools of thought (especially anarcho-communist vs. Marxist-Leninist schools), and know how some might have different interpretations of similar concepts, it can help clear up some of the confusion and apparent contradictions.

(Don't be worried if any of this was confusing, I intentionally picked some of the most confusing cases for dramatic effect! It gets much easier with a little experience.)