Someone once said "There are decades where nothing happens; and there are weeks where decades happen". Can you guess who it was without googling?
Much can change in 13 year but we don't have reliable date to guesstimate the increase of muslim population in east african countries. Kenya claims that muslims make up around 10% of their population. You have uganda with 13% followed by mozambique around 20% and finally tanzania with a whopping a third of their population being muslims.
Of course if you see ethiopia as a non muslim country then i guess that they're around 50% muslim. I already read about some conversion story of many of the native of these countries couple that with a higher birth rate and by 2050 we might see seismic shift big enough to be seen on maps.
There are internal conversion movement in kenya that actively do dawah to various tribes such as the one in the following video.