No, I think they really did mean life-long depression. This particular study might be new, but it's nowhere near the first study that has stongly indicated the possibility that X just completely annihilates serotonin manufacturing in the brain. The hypothesis is that it sort of "breaks open the serotonin flood dam" in the brain; you get completely flooded for 18-24 hours (or however long the pills are good for these days; I know they're not the same as they were 15-20 years ago), but then the lake is gone and the dam's been vaporized.
The only thing I wonder is how much we can trust the researchers, since the British government has desperately been trying to "prove" that Ecstasy is about the most dangerous pill on the planet for years and years. If it wasn't for that, I'd have little trouble at all accepting this hypothesis as probably true. I'm sure never going near an Ecstacy pill.