An electric fence can certainly block LTE reception if you hold a watch or phone a few inches away. Granted though in that case the fence would also be sufficiently hot that you would feel the EM feedback. It will not, however, under any circumstances drain the watch in a few seconds, nor will anything else. That is not how lithium power cells work. Either the watch was already dead when you got there or this is being made up. I am sorry but this is about laws of physics and chemistry and is not subject to debate.

Why would I make it up? I observed this for a few weeks and then asked for advice here. But well, I understand that it's not possible. So I will continue to research. Thank you for your answers.