I had a difficult time understanding the reason for the OP's concern. As I read it--and I might be wrong--the OP seemed to be saying that she called security because she felt excluded from the group.
My thought was that, if this interpretation is correct, it would be interesting to see follow-up posts. The rationale for calling security, if feeling miffed or hurt that one was excluded, does seem a bit outlying. Or more than just a bit, whatever. . . . But the OP can clarify her reasoning.
I would feel uncomfortable too, as others have stated, simply because I wouldn't like being the subject of sets of eyes following me. But unless this was a convention of Ex-Parolees Anonymous, I wouldn't have felt unsafe. It would have been just a temporary feeling of discomfort, and I would have recognized it as irrational--stage fright, if you will--and disregarded it and seen these people as human beings.
I definitely would not have called security. Calling security could only make the problem, whatever the problem might be--unwanted attention? lack of feeling safe?--worse. And it seems ungracious to people who were simply standing there. Evidently they weren't making much noise.
Maybe they shouldn't have congregated there, but people make mistakes, and especially in a group, people do tend to defer judgment to the group. They were at a convention. Minor inconvenience at best, judging by the description and the fact that they weren't noisy.
If the OP was feeling excluded from a convention she was also attending, then she might have joined them. I doubt that the men were deliberately segregating themselves.
But it is the OP's intentions and interpretations, not mine, not other posters', that I don't understand clearly, and perhaps subsequent posts will clarify.
At any rate, no harm done by the OP's choice. We all go through life making very minor misjudgments, and we survive and so do others. This seems to be one of life's many forgettable and inconsequential and trivial missteps of judgment--if it even deserves that category of appraisal.