As I see it, the Pirelli calendar is supposed to be an erotic fantasy, not a factual documentary about Africa in 2008. We could be here all night debating the misappropriation of this-and-that in relation to reality, but as long as the models are mostly naked, then the calendar's foremost requirement has been achieved.
As for his claims of African authenticity, that's the sound of an artist selling his work. His agenda is commercial and he is making the most of this opportunity.
This calendar is recognisably 'Beard' and to people already aware of his style, it's the same stuff he's always done, so I can see why there might be disappointment with it. But this calendar might also reach people who are totally unaware of his work, so for him, it's a perfect means to introduce his style to a wider audience - so why suddenly do something different? He's stuck to what he knows best, to seize this opportunity to reach new audiences.