Screen tearing doesn't only happen if you exceed the refresh rate number. GPU's spit out frames as fast as they can, while a monitor has a set update number. As soon as the monitor wants the frame while the GPU backbuffer is copying it's frame to the framebuffer, that's when you get tearing. If you push 100-144 FPS on a 144 Hz panel, you can't really notice any screen tearing, even though it's happening way more often than on a 60 Hz panel.
The whole don't exceed the refresh rate, is a myth. You get screen tearing both above and below, and like said above, way less noticeable on higher refresh panels. As far as 'source material' is concerned. Videos can't screen tear. If they do, the problem can be traced back to the source. On a 144 Hz panel, 24 FPS look as smooth as it can get on a 144 Hz panel, where as on a 60 Hz panel, it's stuttering in comparison. Regardless wheter or not the refresh rate is 60 or 144, a video in a browser can't screen tear. Some settings is wrong then, or even the graphics driver is to blame. Videos and games are completely different things.