The article makes it sound like this should be surprising
It should not be. Anyone with a clue knows that in a few years there will be no such thing as "feature phones". Even the cheapest phones will be smartphones, most likely all running Android. The cheapest ones may be so low spec they aren't able to do a whole lot more than call and text with some rudimentary browsing, but they will still count as "smartphones" by the current definition.
If you want to see how the smartphone market will look in a few years, just look at the entire mobile phone market today, and all those feature phone OSes (stuff listed as "Java", Series 30/40, etc.) can be pretty much counted as Android, some of the Symbian market goes to Windows Phone, add a few percent to iOS since iPhone will continue to grow a few more years and there you go. Probably 80-some percent for Android, maybe 10% for iOS, a few percent for Windows Phone and a couple percent for "other". RIM will be bought out for it's patents and there will be no Blackberry OS in a few years time.
Maybe the Firefox OS for phones will take some of the low end share that would otherwise go to Android, as another "free" competitor it has a chance of doing so but it's success or lack of remains to be seen. Samsung has talked about doing it's own OS (Bada I think it is?) so given their current hardware market share it could be a decent chunk of the mobile market in a few years, but that's really the only other one that could possibly have a noticeable market share in a few years time.