I agree. I don't see anything remarkable in the video.
They are walking, that's all. And the camera angle is looking down on them (while in the store) and it's not a typical human perspective, so it is easy to read things into it. (By that I mean we are typically viewing people horizontally; not semi-vertically.) They are very, very tall and long-legged and I think they carry themselves in an immature, "colt-ish" manner. (Hand in pocket, buttoning shirt while walking). But I truly don't think there is anything to be derived from the way they are walking and how that might explain anything about them.
The camera that recorded them upon exiting would catch anyone in their least photographic moments. I know I don't walk out of a store worrying about how I look or what expression I have on my face.
If they were at all anxious, I doubt they'd have been in the store to begin with due to concerns about recognition or cameras. They may not know how security cameras truly work, but they'd have to know they were there at all.
Wasn't it George Bush who used to get "accused" of swaggering, and he said, "In Texas, we call it walking". Nothing to be interpreted in my opinion. Not to say they didn't have things weighing heavily on their minds; I'm sure they did. With all respect to everyone's takes on this, I really don't see anything here to be translated into odd behavior or gaits.
JMO and as always, I respect everyone else's opinions as well as learning from all of you.