I bet she was treating the boy anyhow despite the fact that she was known to be 'kind' by her peers. I know how Nigerians act towards people of lower class; it is condecending, arrogant, and not pretty. This goes to show that you should not treat people anyhow just because they are not in the same income bracket as you. They are still people and you are no better than them.
The fact that he is being called house-boy when he is a close relative of her is evidence that she probably did not even treat him with the respect deserving of a human being.
Careful how you jump to conclusions. You may have witnessed something similar with the woman being the aggressor but it doesn't always play the same way all the time.
If he killed his madam because she was unkind to him, why did he try to rape the widowed neighbor?
And remember he's suspected to have raped the madam too because her body was found naked.