There's actually event a "Leaks" template in the instruments app, I wondered why the author didn't use that. And that tool is even documented by apple, see
https://developer.apple.com/library/ios/documentation/Develo...
The author does mention it.
For what it's worth, I can't see what gregdoesit quoted in the article.
Where it fails is when memory is not freed because it's still referenced somewhere from your live objects, but shouldn't be. For example, if you keep adding subviews to a view and don't use the old ones anymore, expecting them to be destroyed but forgetting to remove them from their superview first.
Basically, Leaks is a garbage collector minus the collector, and where it fails is exactly where garbage collectors can fail and still allow leaks. Like any sensible garbage collector, it can handle cycles just fine.
(I know you just quoted it, but I thought this was a good place to address this weird aspect of the article.)