Except it doesn't say what the reasons were for them leaving, or not working. It says nothing about unemployment, just out of employment. Are they retired? are the Students? Are the laid off, are they actively looking but can't find work. The simple fact is the key indicators of the economic strength in the US is recovering are all positive, unemmployment is dropping (for those who actually care to work) job forecasts, are positive, the stock market is rising, and people are spending money again. All signs of positive economic trends.
The linked article discusses nothing to do with the economy it is an article that is discussing the workforce as a whole. The major beef of the article is that men are leaving the wrokforce while women are joining it. With one of the largest factors being the Baby Boomers are becoming of age to retire, either early retirement or of age retirement. Over the next several years more and more of them will leave, and the numbers frankly are not there to replace them. On top of that lots of these boomers were protected by unions, and upon retirement their jobs are not mandatory to fill, robots, computers, other technologies have replaced the need for many jobs.
Of course you would have to be able to read and comprehend basic english to gather that from the article, you saw a flashy intro, and didn't finish reading. It is ok I wouldn't expect anything less from you.