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"Naturally Aspirated" means no enhancements to the induction system. The engine draws ambient air using nothing but the good old vacuum the designer chose to grace it with. The key here is that the manifold never gets into positive pressure ranges.
"Forced Induction" means pressurized air is fed to the engine using an external compressor, typically either supercharged or turbocharged, but I suppose it could include compressed air sources. The key here is that the manifold operates at positive pressures.
Nitrous Oxide is really a "combustion enhancer". It doesn't raise the pressure in the manifold above ambient. N2O replaces normal air, which is only about 20% Oxygen, with a gas that has about 35% Oxygen. In addition, since it comes out of the bottle *wicked cold*, it's quite a bit denser than typical ambient air (I think about 50% denser). The result gives you a substantial amount of additional Oxygen in the charge air, but because it's not delivered to the cylinders in pressurized form it doesn't qualify as forced induction.
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Ram air is grey area.
Nitrous, while adding oxygen content, does not stop the engine from naturally sucking in the air itself.
Forced induction would imply that the pressure inside the manifold is above atmospheric, due to something forcing air into the engine, causing it to imbibe more air than it can on its own.
Since you're a drag racer, I can see why you would consider Nitrous FI; it's not "all motor". While excluded from "all motor", it's still not forcing a positive pressure into the manifold, the engine is still aspirating on its own.