"How?" Link wonders. He doesn't have much experience with traps. Puzzles and mysteries, yes, but generally the Calamity's monsters didn't plant traps. They just hung around until they saw something to attack.

Then there's the other question - how would they know to plant a trap?

"Did they see us?" Link wonders. He didn't think he was spotted. And Juhani being spotted seemed even more unlikely, considering how good she was at being unnoticed.