Demonstrating how to use it: yes is educational, but doing a stress test and just including the software is commercial use as it is one of the main points of using the software. Suppose FurMark were to be paid software, you would need to acquire a license as you use it to test the systems you are working with to create your videos. This same principle holds for OCCT, you use part of it to test a system to create a video. Maybe you could have contacted the owner and discussed the educational/promotional aspect? Yes. But the discussion is the key for the entry into the educational/promotional domain for this type of use.
I'm not saying there is ill will from LTT, someone probably found the software, saw it work well, didn't see the somewhat hidden commercial use licensing and used it. Buying the license is the correct solution now and maybe added policy at LTT to consider the possibility of needing to acquire a license of software used.