Jack trusts McCree's instincts, so clearly this means shenanigans are in play. They're going to need all the navigational skills they can get--Jack is just bitter he's got nothing useful when it comes to getting turned around in caves.

"I'll take whatever you've got."

Sure, it's true that his senses are enhanced thanks to the SEP, but Jack's abilities are waning with age (not that he'd admit it), so he's not going to object to a little boost.