Clearly someone who has never been more an a mile from his house.Africa as a warmer climate requires less technological adaptation. Africans do not need complex houses or full bodied clothing. They can get by readily without metal tools.
Africa is N/S oriented, it has a wide range of climates. Yes, on average Africa is warmer than say Northern Europe, but that is not the reason for the difference in technology.
First, EurAsia is E/W oriented. That means that plants which grow at a specific latitude can be spread through cultural contact along that latitude. More people tending the same crops yields more technological advancements in regards to those crops and more opportunity for that technology to spread/be improved upon.
Second, the distribution of domesticated animals is not even. Not all animals can be domesticated. Cattle, pigs, sheep, goats, horses, chickens, camels etc are not evenly distributed to all parts of the world. With Africa's more severe predator groups and generally lacking domestricatable animals, the various by products of those animals (be it leather, or labor) were not available.
Additionally, domestication of animals leads to disease. Virtually every major disease which effects humans has its origin in one or more of our domestic animals. This will seem counter intuitive but, having those diseases effect your culture is an advantage. Europeans were dealing with several disease for thousands of years. When they reached the Americas, those diseases killed 90% of the native population. It wouldn't have mattered if Native Americans were driving spaceships. You can't lose 90% of your population and expect to keep a culture going.
Third, resources like iron, copper, gold, etc are not universally distributed. You could have the smartest people in the world living on an island that has no iron and they will never get out of the stone age.
It's not that Africans were "hot and lazy". It's that they started off with different access to resources than other groups and as a result advanced at a different pace in regards to the benefits those resources grant a culture.
I recommend "Guns, Germs and Steel". An excellent book that goes into all this in MUCH greater detail