It seems to be the teacher's exercise. It's not connected to Pearson, and nothing suggests that it's third-party supp. material (although I can't rule that out).
At best this is an error in presentation of the material. This starts from neutrality on the issue of human slavery. That's a dangerous line to walk and it requires skill that this teacher does not possess. I agree it's potentially a useful exercise if the teacher is skillful enough. We are talking about challenging the evil-saying of an obvious perfect evil. I'm not saying it's impossible to do that with eighth graders, but it's probably an age-inappropriate method in general, because it requires further instruction on how the South used the "pros" of slavery to justify it, and how that tradition has survived into modern Southern thought. That doesn't scream "Texas charter school" to me.
I do think that either of us could come up with a number of ways to get the idea across more effectively, even using the kind of irony that some people will assume this teacher was going for. The appearance is unquestionably one of soft-selling slavery, as Texas is wont to do. I hope that it's merely unfortunate.