My kids, who are 7 & 9 now, are both pretty good swimmers. Being around the water all the time, we've had them in lessons from an early age, and still send them back for more every summer.
Back when my son was about 2 or 3, before he could swim, we had a close call, and it was just like the article described.
We were at a party where there was an in-ground pool, and all the kids were swimming, including my son, who had "swimmies" on his arms. All of the kids got out to have pizza & cake, and I took my son's swimmies off of him while he ate.
He finished up quick, and managed to get back into the pool somehow, not more than 15 feet from a bunch of people. Just like the article....no noise, no splashing - he simply walked into the shallow end, and continued to walk until he was under.
Fortunately, we saw him very quickly and pulled him out. He hadn't even swallowed any water, and wasn't really scared. Our reaction probably scared him more than anything else.
Me on the other hand...it scared the chit out of to see just how fast something like that can happen.