What are Mr. Douglas' reasons for choosing Colonel Lloyds plantation to write about?

This is a narrative, an autobiography. Douglas spent his childhood on Lloyd's land as a slave; Lloyd was his first owner. It would only make sense that he would include his earliest memories of incarceration at the hands of an owner who expected complete subservience from his slaves. The fact that Douglas chose to share this time, and to admit to the fact that he was treated far better as a child than the adults makes his narrative more believable.