There is no additional context. Republicans don't want to stop being racist, and teaching children that slavery was bad makes them less likely to be tolerant of racism.
That's no additional context. This is a tiny step removed from "they weren't slaves, they were just employees" historical revisionism.
Another part of the curriculum says that teachers need to specify that, while some white people might have caused racially motivated massacres, black people were to blame as well. The Tulsa race riot? It wasn't the fault of the white people who slaughtered all those black people. No, according to Florida's new curriculum, the black people who were slaughtered were responsible also.
The context is that it's true, but only in a limited number of cases. Many African craftsmen were brought here, and many others were apprenticed to white craftsmen here. The vast majority saw the fruits of their labor stolen for the benefit of their masters, but a lucky few were able to make money and in rare cases even buy their own freedom.
Slavery is a complex subject and you have to remember the slaves were strong, smart individuals who would have been constantly trying to make the best of their situations. The fact that some of them had some success in forging their own paths doesn't mean the triangle trade & chattel slavery were any less horrific or criminal.
Frankly, the curriculum reported on is perfectly acceptable, and the reporting is disingenuous. Whether Florida schools will teach it in a balanced way is an entirely different question.