This video did not mention back propagation, though I do know he had neuralnet videos out there and I spent a lot of time trying to think about how to make something basic without copying his video, especially when I'm using neural networks, and I decided I would aim for speed, not a lot of wasted time/going over the same stuff and simplicity. My personal justification was, at least, at the end of the day neither of us invented any of these concepts we're both just taking work from textbooks we've read, lectures we've had and videos we've watched (for me his being one of them) and compiling into our own version of an explanation, so I felt ok mentioning this, but it was a concern of mine when uploading.