The Tarovian neck pinch was a move which Nardole learned from studying Tarovian martial arts. When he used it on Alan, the man was knocked out instantly.
While a skilled Brown Tabard, Nardole could only perform the act with his original right hand and not with his left hand, which was in fact a replacement he had won gambling. (TV: The Lie of the Land)
Behind the scenes[]
The element of surprise - Doctor Who - The Aztecs - BBC
Ixta is powerless against Ian's thumb. (TV: The Aztecs)
The move taken by Nardole is very similar to that which Ian Chesterton used in TV: The Aztecs to defeat Ixta quickly in combat, using only his thumb. It's almost certain that this was the true origin of the Vulcan neck pinch.
The Tarovian neck pinch is likely also a reference to the Vulcan neck pinch from the Star Trek universe, especially since after performing the move, Nardole then remarks "Let's trek on."
The Aztecs aired in 1964, Star Trek tos started in 1966.