Well, what I would do if someone ‘handed’ me a bitcoin on the spot in the form of a key or seed is sweep it into my wallet immediately from my mobile device, perhaps to a wallet that the device I’m holding doesn’t even have the keys to. So after swept, which takes 30 seconds, yes indeed the person has the bitcoin and you no longer have access to it. Think of the time that takes like counting the money in a back alley drug deal. Once dude sees you brought all the money, it’s part time. So it is with sweeping some coin someone is handing you. It must be transferred immediately to be ‘yours’ and ‘counted’