Sort of. That source is one that I occasionally come across and have criticized heavily in the past because it is an example of painting an incomplete picture through statistical manipulation in order to score ideological points. Professionally, I consider it a form of malpractice.
There are a myriad of objections but let's just consider a few. It looks at directly held financial securities rather than total ownership exposure. For example, if you aggregate all of the oil and gas companies in the United States (we'll use them since that is the example I used when mentioning Exxon Mobil), roughly 29% of the equity is owned by pension funds. Those pension funds disproportionately serve the poor and middle class retirees who spent their lives as telephone operators, manufacturing workers, or teachers.
The dividends get paid into the tax-shelter of the pension fund then sent out to the workers who live off that income but have no idea that is where the money originated nor that they, indirectly, own such a huge percentage of the business. In that figure, none of that ownership is credited to them since it's legally removed even though it is absolutely vital to their well-being and they are the legal beneficiaries of the equity. Without it, they couldn't pay for groceries or medicine. That means even though nearly $1 out of every $3 being produced by these behemoths is going into the pockets of largely regular folks, not a penny of that ownership gets credited to them because of an accounting trick; a sleight of hand.
It also doesn't account for distortion created by age breakdowns in household demographics. The United States has a much younger population than many of the other countries to which we are compared. Combine that with the fact that the U.S. is fairly unique compared to places like Great Britain in that a larger percentage of our millionaires are self-made, rather than inherited (and most of the money will be lost in 2-3 generations due to the brutal competitive nature of our free-for-all system), you have the practical outcome that most of the assets in this nation are held by older people who have had a working lifetime to accumulate.
To be specific, as per the most recent Federal Reserve data, the average household headed by a 65-74 year old person in the United States has a net worth (assets-debts) of $1,057,000. The median household in the same bracket has a net worth of $232,300. If you're curious, you can delve through the source material yourself in this PDF breakdown.
Saying, "the top 10%" sounds very ominous but when you look at average families approaching retirement, and you realize that retirees as a class are grossly overrepresented in that 10% figure, it's not nearly as bad as it sounds (though it could certainly be better - don't misunderstand me). Why, precisely, would we expect a 22 year old recent college graduate to have a portfolio stuffed with stocks? They have just joined the work force! They probably haven't even bought a home, yet, if they are demographically typical. Of course your 71 year old aunt holds more shares than you do.
I could go on, and on, and on, but ... like I said: Sort of. It's far more nuanced than it looks.