Bung: Was there longer video that showed where the postie went? To me the only legit reason would be he had 2nd thoughts about the address.
I was thinking this is the more likely scenario. It looks like he suddenly realised that he had misidentified the house number or street name on the letter. Admittedly it's a bit odd that he looks up and down the street.
I'm not sure why he would approach the letterbox if he were planning to swipe the letter rather than delivering it? Unless it was an impulsive last moment thing?