In any case, I don't know anyone who would consider this man to be black. Perhaps it's the lighting or angle of the photo?

Well, like I said. Black is a race, not necessarily a skin tone but mostly identified as a complex and arbitrary delineation of class, nationality, ethnicity, and general skin tone as the easiest identifier but not necessarily the qualifier. I have a white friend who's tan as hell, and studied under a woman from South Africa who was about as tan as my friend. The woman was considered a black woman, while my friend was considered a white man, even though their skin tones were similar.

Life is full of such arbitrary nuance and complexity.

I wasn't speaking about skin tone, but also physical features indicative of African descent. At any rate, in the United States (which is the context of the holiday), class, nationality, and ethnicity don't contribute to perceptions of race; it's effectively the presence or absence of indigenous African physical traits, skin-tone being but one example. Perhaps class, nationality, and ethnicity could be used in 'tie-breaker' cases where race isn't visibly apparent, but that's the extent.

Is who you know relevant?

Yes, because it's a sample of human racial perceptions, but at any rate "who I know" isn't the sample I quoted, it was "who I know of", and the latter is a larger sample than the former. Further, "who I know of" is a pretty good informal indicator given that I know of mostly Americans (and a particularly diverse group of Americans at that). Perhaps you mean "is this sample statistically significant?", in which case the answer is "No, and I never pretended otherwise".