These are the best linear algebra videos I've ever seen. The creator is now working on an introductory calculus series. He's already released the first few episodes to patrons.
Coincidence. FB has over a billion daily users and each one communicates dozens of concepts per day - if each person sees numerous ads per day then it's a statistical certainty that someone, somewhere happens to get an ad that matches up with something they mentioned earlier in that day or week. This is the same reason why everyone has a story about a dream that came true.