I have seen mass mailers trigger these list long ago when that was a norm to communicate I had a site black listed because
even though people sign up for newsletters the can simply report as spam and enough people do it as a opposed to just changing their settings and you have this, its not as common as it used to be for that kinda stuff, now days the content often can trigger reports.
Things are becoming more complicated as power users of large corporate social media are dictating what is hate speech, harmful or dangerous. Long running groups, YouTube, and many others are shut down due to small word usage. Seems if any group is running a socially or politically opposed group meaning they have other sides against what they are representing it can get reported and then is held to what ever standard that company decides.. I could go on as its something I have studied extensively over the years and seen many groups appearing "normal" have issues. Without knowing what Norton is using to trigger this and that it is not on other lists make one think it was more specific possibly in your case.