I mean, why? It isn’t heat-hot, so it isn’t actually melting the snot. Still, when I have a cold the only way I can breath is to down a plate of curry.
It is an irritant. The body says ‘Hot flavoring? Get it outta here!’, so it purges the mucus and the snot doth flow.
I compare the human to a wax candle, and the heat melts the wax which runs down. Metaphorically speaking.