The impulse in all cases appears to be coming from the BNC itself and I ran other tests using different adapters and coaxial patch cords which seemed to show the same thing.
Yes I tried tapping a open BNC connector on the other end of the patch cord, same thing. An even tapping an unterminated coax cable with no connector on the far end does the same. I fact it seems tapping the coax has a more severe effect then tapping the connector. So yes, no escape
I had considerable difficulty testing BNCs without the effect of the cables which was almost always greater.
Maybe it's just me but I was taught that when you are measuring small signals you don't touch anything during the measurement. Not only is this "not a big issue in everyday use" as Dave says but IHMO it's not an issue at all in any proper use of an oscilloscope. Really!
If you know about the effect, and that is the point of the videos. I thought that was obvious, but it seems not, as quite a few have complained the videos were pointless.
There would be a hell of a lot of people who would have no idea it was even possible.
And BTW, it's not uncommon to accidentally bump your scope probe etc (which are very susceptible), and I have seen accidental impulses in real use. Luckily I knew what caused it, others might think it's a real signal, or an accidental trigger could send you up the garden path etc.
It is a real problem in some applications. I have occasionally had it when making single shot acquisitions where I have to set everything up, arm the oscilloscope, and then trigger the circuit or device under test. Usually I end up with a few false triggers while I arrange everything or I give up and instead change the test setup to use a trigger source with low sensitivity.
I never considered it a mystery; connectors, cables, and probes suffer from piezoelectric and triboelectric effects. What I am shocked about is the other examples Dave showed where areas other than the connectors, cables, and probes were sensitive and sometimes much more so; that is just poor and sloppy design. The touch screen example is particularly egregious.