When you "connect" the hot and neutral through the light bulb, you're not shorting them out, but connecting them through a resistance.
Volts = Amps x Ohms
Amps = Volts/Ohms
A typical 60 Watt light-bulb might have a resistance of 240 Ohms. 120V / 240 Ohms = 0.5A.
A length of wire is a resistor, too, but the resistance is so small that we usually ignore it. (Table 9 in the NEC lists this. It becomes quite important for voltage drop & arc flash calculations.) You're only talking 2 Ohms for 1000' of #12 wire. Or 0.2 Ohms for 100'. So, if you actually DID wire-nutted two 50' lengths of #12 (100' total) and flipped on the light switch, you'd get 120V / 0.2 Ohms = 600A, and would trip the breaker and maybe burn something up.
Since you didn't blow anything up, something's disconnected. Maybe whoever nutted the two together did so while doing continuity tests to try to identify where the neutral was open? It's the first thing I would do if I suspected there might be a break in the cable at some point between the two boxes. (Well, 2nd thing; I'd disconnect the neutral in the light switch box first!)
