Yes i was thinking along similar lines. Also given the scenario requires physical proximity of sender and receiver, the payer already has internet access at that moment, which makes several things possible.

To be fair, iirc, this was the *exact* application of ecash that was imagined by people like Chaum, Brands etc. in their original papers (vendor in meatspace has network access, customer doesn't) so I'm definitely not claiming this doesn't make sense.