I just wanted to add to this thread: There are quite a few people who have said that there can be no native writer from Kenya, etc. Well, I'm Indian, even though I have moved to Germany recently. Also, I'm a native speaker with English being my mother tongue and it has been so for generations, very likely more generations than some US citizens. My grandparents taught English in Uganda and there were quite a few local families that spoke English as their first language. Of course, there are going to be some regional changes to a language, you see this when you compare US and AUS English to UK English. So the ultimate question is going to be what you consider native.
Of course, this guy who applied is not a native speaker, I'm not arguing against that, but if you are seeking native speakers from specific countries you are allowed to say so on Upwork, many people do. I have applied to such positions and very often I was chosen over the others, even though I charge more than some of the others in many instances. It's been a while since I've worked there though, the quality of job offers had reduced drastically compared to when it was still Elance (prior to the merger with oDesk).
The good thing is that most of the quality clients on Upwork know what they want and they judge a person by their work and not where they are from, this is already evident in the proposal as we see here.