"Who wouldn't hate those kind of "get ambushed in the street" things?"
Given it was a Labour supporter, rather than some "plant" wanting to make trouble, it seems rather odd that he would feel "ambushed". Certainly it sounded like she had asked pertinent questions (I am perhaps the only person who has not seen any of the TV coverage, but did hear the piece of conversation from GB in his car, as it made radio news for hours, of course).
Seems like something of an "own goal" as he apparently left giving her normal pleasantries and then like a hypocrite, slagged her off once he thought he was out of earshot.
It's understandable he'd be contrite, if only because otherwise all Labour voters might consider him two-faced and be worried about anything he said in public, and whether he means it truthfully, or not.