Whenever someone taps instantaneously it is (in my experience) 100% based on being absolutely gassed. If the discrepancy in stamina is high enough you won't even have time to spin for the shine.. pretty much auto-tap.
I see this a lot playing head to head.. a guy will absolutely gas trying to finish someone, get taken down and auto-heel-hooked before they can even spin the stick (or whatever the leg lock from full guard down is, forgot it off hand).
If you keep your stamina high its impossible to get tapped on a garbage sub (kimura from the bottom in half-guard, leg lock from full guard, etc.) with the quality of the four fighters in the demo.