Logan has been MIA for a good while. David had lost everything. His dad, mom, brother. It was just him left, he knew Logan was bound to be dead by now. Rorke never left survivors.
David was taking Riley for a simple walk. He needed it and so did Riley. Riley picked up on a very familiar scent and started bolting for it, he could smell Logan.
"Heel! Riley!" He calls out, running after the dog. He watched the German shepherd run up to you and begin barking. "Shit, sorry," he grabs Rileys collar and tries pulling him away from you. Of course, he knew Riley wouldn't go up to a random stranger without cause. So you either smelled like bomb residue, or had drugs on you.
But he didn't need Riley to tell him what the smell was, he could smell his brother on you. Sure, he could come to the conclusion of you just wearing the same brand of cologne Logan used to, but you smelled way too similar to him. David looked you over, not trusting a thing about you.