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Description in that article is very bad. How can you get correlated photons from some classical light source? Like, you get two random photons and they happen to be correlated?

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It's not bad, it's wrong, since they make reference to the "entangled photons in the light coming from the quasars," which is entirely not how the experiment worked. The light from the quasars (which weren't measurably entangled with squat!) were essentially used as random number generators, in order to perform standard Bell test experiment [0] using a standard laboratory entangled-photon source.

I recommend reading the paper instead, if you're interested [1].

[0] https://en.wikipedia.org/wiki/Bell_test_experiments [1] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...

There's really no such thing as a "classical light source". Rather there could be an explanation of observed behavior derived from classical mechanics. What the experiment seeks to do, and claims to have done is to make an observation that can only be explained through non-local quantum entanglement.

It's the explanations that are "classical" or "quantum mechanical" not the things in the experiment.

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