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Question: Four quarks, or two quarks & two anti-quarks?

Answer: Not anywhere in the Scientific American article. Also, not in the abstract of the paper. Actually have to read the paper, to find out that the claimed tetra-quark is 2 quarks & 2 anti-quarks.

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Pretty sure you can't have one with 4 quarks, there'd be no way to make it colourless (so it couldn't occur in isolation). It seems 2 quarks and 2 anti-quarks is the only possible combination.

The paper probably considers this 'basic knowledge' which is why they didn't mention it in the abstract. Not sure why the Scientific American article doesn't mention it but maybe they didn't want to explain colour charges.

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