Maybe, just maybe the problem is us.
When we encounter someone we do not know, how do we assess them? How do we know they’re Yidden, how do we know they are Shomrei Mitzvos, etc.? I postulate that the average means of making such assessments is based on the externals. The manner of dress, and other outward signs. And there are many times that such assessments are accurate. But sometimes the are not. And the errors go in both directions.
We can see a manner of dress that doesn’t fit our current expected norms (white shirt, suit long or short, hat of whatever kind, etc.), and when these don’t meet our expectations, we reach conclusions that the individual is not frum, or just not one of ours. When it does, we then assume, as seems to have happened in this case, that the person is a newcomer from another frum community.
The issue is that we base our conclusions on an erroneous base – chitzoniyus. But that has been the trajectory of our community, where more attention goes to these aspects, and far less to the ones that matter most. Food for thought.