Thanks to stifle's clarification (and memory now of when they usually "lifted" a paper ticket coupon), I sort of get it now. Except I still don't quite understand how he'd get both boarding passes, unless he in fact checked in at the airport check-in/bag drop with both tickets, proceeded to boarding area, handed the economy boarding pass with paper ticket to the boarding agent (at which point they'd lift that coupon), tucked it away, pulled out the F boarding pass (but kept the F coupon that hadn't been lifted out of site), presented it to the cabin crew... all a bit complicated.

And, indeed, I would think that by the time the manifest was completed and the doors were closed, it would seem strange that the numbers in each cabin wouldn't have matched.

Between the eventual passenger manifest not matching, and the fact that to get both boarding passes he would at some point have to have completed initial check-in for both tickets (which would have been at practically the same counters... unless he checked in using one ticket at the economy counter, walked over to the first counter and checked in there... all getting a bit thick, methinks)