"Insulated" is a strange word to use there, but that reads for all the world like "This was a one-off project for me I don't really work on anymore".
Many academics end up having those. It doesn't mean anything about your research, and definitely isn't "shocking".
To respond to your edit, one-off or isolated projects aren't inherently better or worse science than any other project, so there's no reason a top tier journal wouldn't publish someone's side study. Indeed one of my best publications is from a one-off project.