^Flase-negatives exist.
Also; if you were drinking or something like that you may be lucky enough to detox yourself. As I doubt you inhaled a massive amount anyway; but still possibly enough to get high. Although you never said if you felt high or not, so I can't assert anything.
However, don't people say Cannabis smoke goes "stale" after 8-10 seconds? If this is true then I guess they don't exist, since you're not inhaling the smoke the second it's burnt, but merely breathing in second hand smoke that's been stored in someone lungs for a time and then left to hand around in the air for a bit.