Well it's saying that he grew up in a culture where having slaves and killing people was the norm. Later he was forced to live among those he had been led to believe were far beneath him, watch his mother die due to lack of resources, and was rejected by those he considered his own kind. It also shows he was always fairly driven seeing as he chopped off his own father's head as a child.
It's not a bad backstory it was just told very quickly. We have also been getting hints of it for a long time now. I think the rest of his story will be combined with Law's as the actual flashback to come is likely to be about Corazon.
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