What is ironic about the stolen sneakers?

Much of Holes is written in an ironic tone, and irony is much in evidence in this particular part of the story. Stanley has been sent to Camp Green Lake for stealing a pair of sneakers he didn't actually steal—they fell on top of his head from an overpass as he was walking home one day. It turns out they'd been donated to a homeless shelter by his sporting hero, Clyde Livingston, who wasn't best pleased about his donation being stolen.
What's ironic about the stolen-sneaker incident is that it illustrates the false impressions that just about everyone has about Stanley. The prosecution don't accept the likely story that the sneakers just fell on his head from above (though they did); the guards at Camp Green Lake don't believe for a minute that he's innocent; and the boys in his tent are pretty certain that Stanley wasn't arrested for stealing sneakers.