Mini cloud of stuff that hasn't been around since big bang.....
What they mean by that is simply this. The form of matter that they were able to make takes such a large amount of energy (in this case, from a Relativistic Heavy Ion collision) that it probably hasn't been seen naturally since the big bang. It also doesn't stick around for long in such a form.
The "explosive" results are interesting. Like quark fusion or something analogous maybe....