I didn't say it was rehearsed.
The computer screen could have been used for Google Classroom, Zoom, Teams or another platform to share with those at home. It could also have been used for pre-prepared presentations with Powerpoint, Loom, genial.ly or something else, which is what I do with my own online pupils. I also sometimes link to online teaching teaching materials via Zoom, as part of a lesson. Many teachers already make use of online materials provided by publishers such as Pearson or Oxford University Press. BBC Bitesize and Oak Academy have been providing recorded lessons. The teacher could be integrating those into her lesson.