How is that remotely the same as actual depression? It's an insult to people who suffer from this medical condition.
Looking for the study itself (which I can't seem to find), but the article says something along the lines of "showing symptoms of depression". Symptoms of depression are often caused by depression.
No, it's not an insult at all. The biggest insult to depression sufferers is not recognizing it as a condition or implying that they are something other than depressed.
Edit: I'm sorry; perhaps you are simply not understanding the article. Is English your primary language?
The only difference is that (heavy?) Facebook users are more likely to suffer from it.
If you want to argue against it, I recommend you say that the actual mechanism/cause is on shaky ground.