Link's first thought, after crashing to the ground with a thud--and rising to his feet to make a few agile backflips out of the way of the fire--is that he must have done something to anger the goddess, if he's stuck in a cave full of fire-resistant bugs of fire and all he has to defend himself is a sword and a wooden shield.

Either that, or she's testing him, perhaps for some ordeal where he finds himself in a dangerous situation with barely anything to protect him. Or nothing at all!

...like that's going to happen.

Sword drawn, he observes the fireflies, thinking of a way to attack them without endangering everyone--or himself.