For Uhuru to win such a case is akin to climbing to Planet Mars on foot without a rocket.
If Muthama was speaking about The Pope there is a chance. Uhuru has been making similar utterances and it is easy to prove that Muthama's statement was in the general mood set by the president. Uhuru would be asking the court to judge others on a higher standard than himself - which simply won't pass.
As for slander, he would have to show that he is entitled to greater respect than Muthama subjected him to. That would open a pandora's box where his previous utterances -
shetani, etc - and even other "Presidential 'vocabularies'" such as
Mavi ya Kuku, Kuma ya mamako (his father - 1973 and Kibaki - 2003) etc would come up to help determine whether Muthama has strayed from the general mood. It is a waste of time.
Its more like slander because its spoken, however, its very difficult for a politician to win a slander case. It is definitely not hate speech but since the supreme court has not clearly defined what hate speech is, that is all they have on him. The hate speech statute is so broadly defined and its constitutionality v. free speech should be litigated to the supreme court so that the court can draw the line to avoid abuse by the state.
I watched the speech live and now again. I see no hate speech. There is possible libel which is no longer criminal but civil. Uhuru can sue Muthama privately and not abuse his position to settle what is clearly a possible but very distant case of private injury