Question regarding killing Shadow Servants

I’m doing some farming right now on the Nitocris node. You know, the one with the Demon and Shadow-Blackbeard as final enemies.

So I did an NP with Nitocris, 300 % overcharge with is 50 % Death chance.
And somehow Blackbeard died instantly.
That’s why I wanted to know: Shadow-Servants? Do they have a higher instant death chance then normal Servants? and the wikia says that it’s either unknown or dependent. I’m guessing it’s based on the servant’s death chance themselves I guess. You got lucky.