That photo is definitely creepy. I do think the tactic might work at times, because I do think the squeaky wheel gets the oil at time (I know the wheel in this case is silent not squeaky, but you know what I mean....people do tend to get their way sometimes just because they are annoying). However, that doesn't make it polite.
However, I don't think the behavior is at all threatening, just annoying. Standing to the side silently is not a threat. I think calling security because someone is standing close by would be quite an overreaction. I also don't think that I am obligated to sit down just because some airline employee tells me to. They do not have any authority as to whether I sit or stand. I am not talking about TSA, I'm talking about random airline employees. They do not get to tell me what to do, other than "please step aside so I can help the next customer". That is ok. Telling me that I need to sit, no. I will sit if I feel like it, or I will walk around, use the restroom, or grab a bagel. I am in NO WAY obligated to "obey" them. They don't have that kind of authority.