Answered

The researchers found that about 90 photons had to enter the eye for a 60% success rate in responding. Since only about 10% of photons arriving at the eye actually reach the retina, this means that about 9 photons were actually required at the receptors. Since the photons would have been spread over about 350 rods, the experimenters were able to conclude statistically that the rods must be responding to single photons, even if the subjects were not able to see such photons when they arrived too infrequently.

Piecing these and your findings together, it hints to an interesting sub-question, what do we really mean when we ask the original question?

Can the human eye physically detect it? Seems like…yes?

Which suggests the subsequent physiological thresholds involved, various human signal processing chains etc. What a fascinating topic.

The choice of a 60% success rate is an interesting one, too.