He may well be processed the same way. I'm talking about the ease of CBP determining (a) his identity, (b) his most recent origin, and (c) his nationality.

If they know which flight he was on, it's quicker to work out who on that flight hasn't gone through CBP yet. If he hides in the restroom after his flight until dozens of other flights have arrived from all over the world, then presents himself at the CBP booth without a passport or any ID papers, it's a lot harder to prove who he is and where he came from.

As I understand it, someone coming directly from their country where they were facing persecution is treated more generously than someone who has been living in (or even transiting through) a third country. A refugee from Sri Lanka is going to get more serious consideration than a refugee from France. Someone fleeing southeast Asia via the UK and then Canada is going to have to explain why they didn't seek asylum in those countries.