I'd appreciate if Dan would chime in, but I think it likely triggered the "Flamewar Detector". I think this is based on a ratio of Upvotes to Comments, possibly adjusted by flags, but I don't think it's been fully described.

This isn't a perfect system, as sometimes contentious conversation can be better than non-discussion. But overall it's probably a good to have a temporary throttle until a moderator can make finer grained fixes.