it's not 10% market share. It's whatever percent usage share.
That means if no one in Guinea has internet and you want into Guinea and load a web page on your iPhone, that means it's 100% usage share.
If there are 100 people who visit 1 page, and you with your iPhone visit 100 pages, then suddenly it's 50% usage share.
According to CIA Factbook there were only 8000 people in all of Equatorial Guinea who had internet access in 2006. Such a small number, means that one or two iPhone users could influence the percentages if they were particularly active. A few business travelers could be responsible for it.
Which is evidenced by the 2% -> 11% jump in one week. I don't know what internet access is like in Guinea these days, but a few years ago there was 1 ISP and it had 64Kbps/s bandwidth... which is slower than EDGE.
Wirelessly posted (Apple Communication Device: Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420.1 (KHTML, like Gecko) Version/3.0 Mobile/4A93 Safari/419.3)