No. It is comparing different things. The percentage of Americans who own stocks is different that the percentage of stocks owned by americans. Say 90% of americans "own some stock" but they are dirt poor. Their share of the total stocks available could well be 1%. The rich 10% then own 99% of the market AND 90% of the population own some stock. One fact does not negate the other.

Remember that the median income in the US is about 30k. If you have any sort of actual pension plan, there is a good chance you are in the top 10% in terms of net worth.