As a further clarification to the video, the trigger sensitivity levels are two boundaries that the signal transition must cross. If the signal fails to cross both boundary levels, then no trigger is found. As explained by BenF, you can set the trigger sensitivity to zero and it no longer conditions the trigger findings, and then only the trigger level affects the trigger findings. The video does show you how to adjust Trig Sens. The lower right hand context sensitive display window will show the sensitivity value as you change it. Because the Trig Sens is usually adjusted to be a much smaller value that the Trigger level, then it would be very sensitive to V/Div changes.
This trigger sensitivity feature is normally used to generate a single display sweep when some abnormal portion of the waveform transcends the normal waveform pattern.
EDIT: In the above paragraph I removed “touch” because I went back and looked at the code and it must cross (exceed not just equal) those parameters.