"So that means when you said those words..."
Lugh nodded in confirmation.
As for the words she was referring to, it was naturally when he yelled,
"Stop! Vaelith..."
followed by,
"...Vaelith called her a Sylph."
The first part of the sentence was a message to the elf lurking nearby, undoubtedly preparing to act when the priestess threatened to destroy everything, and everyone, nearby.
The second part was a warning, subtle but clear.
Her main body is most likely not anywhere near the vicinity.
It was a coded signal for the elf. There was an enemy present. She shouldn't reveal herself.
Lugh had intentionally made himself the highest-priority target, hoping to draw the enemy's wrath onto himself.