The about page at https://alllooksame.com/about/ seems to indicate that the author who is of Japanese descent is not able to differentiate between them himself and made this website to test the assumption

In any case, I thought the "you all look the same" racist trope is that east asian people look similar to one another individually? is there an actual expectation of being able to tell the actual ethnicity/countries apart?

My recollection is that this website says that a 50% score is bad when the expected value of random chance of picking the correct option among 3 is 1/3. A 50% average score means there is some signal there. If it was impossible to guess, the average score should be 33%