Notice that Luke says 'get' not 'have.'

The Scent ability Luffy mentioned is possibly relevant to what he does next...

I imagine it's like "Wait, they're mirror images and I only gotta pick the right one?"
(Uses Scent)
"That one." :punches:

Either that or "The voice of all things" that occasionally pops up when he does some inexplicable feat of perception

Or it's some dumb luck thing where it's like "Really?!?"