Exasperated IMO from a heavy smoker just walking. BG may have had a fast pace walk to keep Abby and Libby from rentering the south end of the bridge and getting back out into the open. Also.... some people can sound exasperated as a nervous voice or even excitement.
BG speaks the words as if he's so laid back and relaxed that he's half-asleep. I know people can sound exasperated in different ways, but I've never heard it in this particular way. It still sounds like he's trying to sound friendly and non-threatening at this point in their meeting -- as if he's trying to lure them calmly into thinking he's just a nice guy.
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