Would this be considered plagiarism?
Plagiarism is taking the work or ideas of others and presenting it as your own. If you have a sub chapter on topic X and somebody else has a sub chapter on that too, that doesn't make it plagiarism. E.g every 2nd grade math text probably has one chapter on addition and one chapter on multiplication. That doesn't mean they are plagiarizing each other, it's just the natural way to split up the material. What would be plagiarism is if you got the idea to have a sub chapter on topic X from reference Y but you did not cite reference Y and you made it sound like you personally came up with the idea of a sub chapter on X on your own. As long as you've cited your sources properly you should be fine.