Eh, I'd say when used correctly it is one of the most cunning identifications possible. Like with anything, overuse or overly broad use is where the problem is. For example, in some circles "that's ad hominem" is just about the most useless thing you could say because it's being used overly broadly (ad hominem is when your argument is actually to discredit your opponent by maligning their character rather than the substance of their argument; in circles like I'm mentioning here, countering someone's points and then calling them a fuss-ended bus-widget might be mislabeled as ad hominem).
A good example of concern trolling that I see almost daily is someone dumping on a fat person who eats well, exercises daily, and whose doctor says they're perfectly healthy. "I'm happy you're happy but aren't you worried your unhealthy ways are going to catch up to you? I want you to live a long life, not die in ten minutes." Slight exaggeration on the form in the second half of that last sentence but otherwise fairly par for the course.
Having not delved into the original context, I can't say whether or not I'd agree concern trolling was actually going on. But I'm not the final arbiter anyway.
EDIT: Having now read the context, I don't see a point for the thread to exist in its current state and also don't see the thing being accused of concern trolling as concern trolling. Don't feel like delving into that conversation and where I fall on it but I think the "concern troll" in question responded in pretty much the same tone as OP and therefore qualifies as a smackdown. Again, not making any judgments on the merits etc. of either side.
Further edit: I'm not saying the original thread should be deleted. Simply that it's not clear why it should have been made on BBS.