If you as an individual has visitors who come to your house and snap pictures of codes in your devices... I wouldn't be more expectant of Zigbee or any other standards, rather I would be more keen on the visitors I allow into my house.

That shouldn't do them any good. The device should require it to be in pairing mode for the key to do anything.

But then what do you need the key for? In theory somebody else could try to pair with it while you have it in pairing mode, but they would have to be on your property for that and could potentially see the key anyway. So you go slap them with a trout or call the police or something, and then go back to setting up your future garbage.

So that that initial pairing is more secure.

Zigbee etc. tries to get around the whole thing by requiring that the pairing process is done from a 5cm or something distance.

Imho that is good enough but I don't know how far you could extend it with directional antennas etc.

That anyone can reclaim a device they hold in their hand is a feature.