fathom - 3:28 pm on Jun 2, 2013 (gmt 0)
If so, am I a victim of negative SEO as I NEVER did any link building?
Assuming that negative SEO is the cause of any drop also suggests they were the firm that produced the ranks you had 'unfairly' in the first place.
Implying you got ranks and never did anything rarely works so if you indeed built the ranks... then you did it with less desirable links and those caused the drop even if the alleged culprit did a reverse spam report on you. (It would have been far easier and more effective for them to simply report your webspam to Google).
This does not work if you are an actual victim as you can't lose what you never had to begin with.