What you see on the status bar depends on your operating system. Though Safaricom has 4G+, it is the bare minimum which supports a data rate of 150Mbps. Most global operators today talk about 4G+ when they deploy LTE CAT 6 (300Mbps.) Maybe that’s what your phone will show as LTE+ or LTE-A or 4G+. Your speeds seem like you might be using 4G+, though.
Also, Safaricom is using 10 Megahertz of the available 20 Megahertz on both bands 3(1800Mhz) and 20(800Mhz) so theoretically they have as much bandwidth as all the other players combined. In short, it looks like Safaricom has been given 50% of all available bandwidth of the LTE spectrum. They’ll therefore be able to push more data but on the downside, they have more than 70% of the mobile subscribers in the country.