That was weeks ago. And no great loss, they weren't in very good shape.
Hang on, so he'd been training in his Crocs then?
Err, no. Not a lot of training had been going on.
Not running, at least. "I did a few smaller runs, and two longer distance runs, but that was a while ago."
Yet Callum managed to finish 10th out of more than 1200 people in one hour, 23 minutes and three seconds.
Thirty minutes faster than his time in the same event last year, although that was more a fun run. Turns out, this is one fit teenager into cross-training. Mountain biking. Surfing. Hiking.
In fact, he wore his Crocs on a hike of the Cape Brett track this year.
That was the definitive factor when choosing whether to run 21.2km in his Crocs or school shoes.
He was pleasantly surprised at the Crocs' performance.
The straps kept them on, and there was only one blister. Crocs don't have laces, so the timing device - a transponder - entrants tie to their shoe was slipped into his sock.
"I think it (the blister) was the transponder rubbing on my foot."
Fellow race entrants and Callum's mates greeted his impressive effort with a mix of head-shaking amazement, or observations that he was slightly mad.
He'd run in them again, and reckons Crocs - maligned as a fashion item - could reinvent themselves as a sports shoe. "Definitely, just watch out for the transponder, and wear some socks."
