you keep turning the world upside down.
what do you do with the human sympathy of perfect strangers when the only person you cared about at that moment rejects you?
let's assume it's a heartfelt declaration, because otherwise it's simply a joke in bad taste. we're not talking about a marriage declaration between two people who already have a more or less solid relationship anyway, it's a leap into the void without a safety net
if you think that a girl accepts in order not to make a bad impression with strangers you are extremely optimistic, at most a more sensitive (or calculating) person would not respond by moving the discussion to a more private place.
you might be right if we were facing a marriage request between two people theoretically in a more or less stable relationship, in that case the public request can force their hand, but here we are talking about two guys who still have to start their journey.