How much does he know gets a quirked eyebrow but nothing more - he's not about to pry into someone else's secrets. If it doesn't pertain to him or the situation at hand, then he's not about to waste time on it (though he will be curious later, when things are less dire). "Well, if it hadn't come and found me, you'd still be down there with whatever this is in your neck." He's still holding on to the device. He's not sure what to do with it yet - maybe there's someone around who can make use of it. Reverse engineer it, use it to fight off the Forerunner, something that's outside his skill set.

"Get your feet under you," he says instead, leaving whatever secrets are happening here alone. "I'm gonna put you down."