This probably won't be a popular opinion, but from a truly objective standpoint, I think it's possible, for the same reason that non-blacks are a standard deviation worse at athletic endeavors. Two factors of evolution point me to this conclusion. Europe became civilized long before Africa, which I would guess leads to a natural selection for intelligence in Europe (as opposed to physical abilities in Africa - hence better athletic abilities for them) starting longer ago than in Africa. The second factor is Africans' earliest days in America, when they were actually bred for physical ability while the intelligent dissenters often were killed or not encouraged to have children.
See, I told you it wouldn't be a popular opinion. I don't think it's something that should just continue to be ignored, though. Turning a blind eye to possible facts just because we don't want to believe them doesn't make them go away.
Immunity to disease was much more strongly selected for than intelligence in Europe. Hunting requires more intelligence than farming, so intelligence was more strongly selected for in Africa. That modern African Americans were descended from slaves bred against intelligence is more likely to be true.
However, even if that is true, it still may be the case that some small amount of bias does indeed exist in IQ tests. For example, I was given an anecdote about a Chinese boy, who, when shown a picture of people using umbrellas on a dry day and asked what was wrong, responded that nothing was wrong with the picture. Apparently he interpreted the umbrellas as parasols, something Americans would be less likely to do.
Regarding your first point, you're probably right, and I likely overstepped my ideas and/or didn't express them completely. I also had another consideration that I didn't express in my first comment. The Africans that ended up as slaves in America were the ones who had been defeated in tribal battles. On average, I would say they would likely be less intelligent than those who win battles or avoid them altogether.
Regarding intelligence of agriculture vs. hunting, I would argue that hunting may require more skill, but in agriculture, intelligence (and creativity) has a greater reward (than in hunting). That is, it is very difficult to automate tasks in hunting (beyond things like inventing guns, which they obviously hadn't done), but agriculture has been steadily getting more efficient with creative inventions from iron tools to plows to the cotton gin and so on. Hunters today still use very similar methods to ancient times. For that reason, I believe that an agricultural society selects more strongly for creative thinking, while a hunting society selects for physical skill and quick thinking. The creativity required to change society in order to accommodate more crowded conditions also undoubtedly requires intelligence. Anyways, enough of that...
I do agree with you that there is likely a small amount of bias in tests like these, and your example is a good one. Another I have heard was about a question which involved the "knowledge" that lemons are yellow. In Latin America, however, lemons are more often green, obviously giving Latin Americans a disadvantage on that particular test question.
See, I told you it wouldn't be a popular opinion. I don't think it's something that should just continue to be ignored, though. Turning a blind eye to possible facts just because we don't want to believe them doesn't make them go away.