Please don't read the article and instead just guess what they did. You are in fact entirely wrong: they use that the same muon passing trough two detectors, so

Please don't read the article and instead just guess what they did. You are in fact entirely wrong: they use that the same muon passing trough two detectors, something that happens by chance, and you can identify by knowing the geometrical distance between the two detectors and convert to a very narrow time window during which you accept signals.