Here's my view:
Yes, the cc should have checked the screens before the demo - its a CAA requirement (for UK based airlines) that all pax are informed about safety procedures (safety demo).
I've known outside temps to reach -50C transatlantic.
On most aircraft types there is a small indicator window to be able to see if the door has been armed / diarmed. Well trained CC would be able to spot it at 20 paces. Some airlines will have their Senior CC check it a third time.
Enjoy your jollies & stop thinking about airline nonsense!
