First of all, sorry for this.
I alerted the moderator in question for clarification.
While I do not have the details myself, I can give you the most likely explanation.
We are getting a lot of sign-ups from spammers. Some of which, will use the accounts much later for spam, some sooner. We use various techniques to try and detect those accounts as early as we can. Some of the decisions are based on heuristics.
In this process - unfortunately - every now and then we mistake a proper account for a potential spammer. We try to minimize this, but we can't entirely prevent it.
So I guess something about your registration (and it may be something that was not even under your control), will have triggered said heuristics.
If there is any other reason to what has happened, the moderator in question will probably add to my explanation in the next day or two.
Again very sorry for your first experience. And welcome to the forum.