I still dont see why this would be a surprising find in any way. That teperature seems very pleasant and conductive for life. Maybe the extend of the ecosystem is what is shocking? Why point out a relatively normal temperature then though?
The article is somewhat confusing but I think the surprising thing is that the ecosystem includes species that are known to be extremophiles that are part of vent ecosystems that have very different conditions than the newly-discovered below-the-vents ecosystems, and which it was previously unknown how they arrived at new vents, almost immediately when the vents form.