It was more than likely pruned but kept on the forum. Staff can still see everything though.
As a former staff member, I can tell you that there are very few posts that are actually deleted. Most things that disappear are simply hidden, and only accessible to staff members. That thread has -1 reply because of what Strategist said, so yes it is possible .
Aah okay, thank you for the information. I had an inkling that the posts had been hidden from public view because I don't think the forum software would actually like it if the thread was actually empty. So long as the mods/admins can see the information, so that they can refer back when required.
And btw, I have one last question: can moderators and admins still receive warnings, suspensions and bans? Because I thought that the last member to receive a warning was a mod?