@Qmechanic Well, he had his production team go through creating an image with those words, to be placed in the background. I took a screenshot.
i.stack.imgur.com/SpV0J.jpg So it's definitely not a simple slip. Here is my hypothesis: Matt wrote the script for that show together with a collaborator. They wanted to see a connection between Fermat's least time and motion of matter. And then a thought occurred: hey, GR has time dilation. Fermat least time <=> Principle of Least Proper time.