Someone correct me if I am wrong, but I think the position of Secretary to the Cabinet was separated from that of head of civil service...effectively, there is a Secretary to the cabinet and a Chief of Staff whose roles are distinct:
Quote:154. Secretary to the Cabinet
(1) There is established the office of Secretary to the Cabinet, which is an office in the public service.
(2) The Secretary to the Cabinet shall--
(a) be nominated and, with the approval of the National Assembly, appointed by the President; and
(b) may be dismissed by the President.
(3) The Secretary to the Cabinet shall--
(a) have charge of the Cabinet office;
(b) be responsible, subject to the directions of the Cabinet, for arranging the business, and keeping the minutes, of the Cabinet;
(c) convey the decisions of the Cabinet to the appropriate persons or authorities; and
(d) have other functions as directed by the Cabinet.
Thus Kimemia role is that of a secretary, literally.
Kinyua is the head of Civil servants which was previously a role that was played by the Secretary to the cabinet.
Article 132 (4a) "The President may establish an office in the public service in accordance with the recommendation of the Public Service Commission"