That's fair, could easily be one of those instances where one guy is hoping to hurt the other but not actually injure him. Kinda of how when a player throws a massive hit on another player, I think the desire there is the they get rocked, gently skate back to the bench and miss a few shifts getting the cobwes out and then go back out on the ice a little timid because of the hit. They don't actually want to injure someone. It's a fine line though, that mentality can easily go too far and have very real consequences.
I'm reminded of Bertuzzi/Moore incident, I firmly believe Bertuzzi was trying to put some serious pain on Moore, he wanted to rough him up to say the least. Did he actually want to cause him a neck injury and end his career, no I don't believe that at all but intent or not, that's what happened. Also the McSorely/Brashear incident, the former was definitely being a dick and hoping to ring Brashears bell with that stick swing but I don't at all believe he wanted much less expected Brashear to collapse to the ice convulsing. As you alluded, a very "oh f***, what have I done?!?!" moment.
Perhaps that is what happened here (I still have not watched the video), the player swung his foot thinking he was going to ring Johnson's bell with a kick to the head but instead delievered a lethal cut to the throat. If that is the case, I would expect an involuntary manslaughter type charge to occur because while I highly doubt he intended to even cut Johnson's neck let alone kill him, the end result was still the loss of life.