you said you can't kill someone (generally) just based on them saying something. that statement is nonsense.
in THIS case i mean goddamn it .. it wasn't just a verbal was it .. he had scissors to the mans throat PLUS verbals.
and finally your own link says
"1. A person may, subject to the provisions of subdivision two, use
physical force upon another person when and to the extent he or she
reasonably believes such to be necessary to defend himself, herself or a
third person from what he or she reasonably believes to be the use or
imminent use of unlawful physical force by such other person, unless:"
that covers verbal threats because it allows for a verbal thread of a future physical attack that has not happened yet.
so if i say I am going to shoot you and it is both an imminent and credible threat then you could shoot me first.
just a credible threat alone could constitute an assault.