For their more recent data they reported seeing ~32000 solar neutrino events over a 1600 day dataset (cite: top-right of page 13 https://arxiv.org/pdf/1606.07538.pdf). Their detector nowadays is more sensitive than it was when the OP was published so I would estimate the image comes from probably around 5000 neutrino events.
And I don't know any specific numbers but you can be sure a large amount more of neutrinos interacted with the air/rock between the Sun and Super-K than interacted in the detector volume. But that number (whatever it is) is still tiny compared to the total flux (which is ~5 million per square centimeter per second).
And that's of just the "high energy" type neutrinos that Super-K is sensitive to. The lower energy varieties are more like 10 billion per square centimeter per second.
And I don't know any specific numbers but you can be sure a large amount more of neutrinos interacted with the air/rock between the Sun and Super-K than interacted in the detector volume. But that number (whatever it is) is still tiny compared to the total flux (which is ~5 million per square centimeter per second).
And that's of just the "high energy" type neutrinos that Super-K is sensitive to. The lower energy varieties are more like 10 billion per square centimeter per second.