If you are "average", you will sound like an AI, because an AI is the average of its training data. I don't think it's only Kenyans; I've seen the same distinctive "dialect" from many others.
The "voice" of chatbots comes from the stuff after the main training, which is very different to the average human voice. Even the main training would give you something like "average on the internet" voice, which is quite different to the average human voice.
