I’ve done a few events, and I have to say, while you’re in the midst of an event, it can be hard to have any idea of how far you’ve gone, so it could have been an honest mistake, took a wrong turning somewhere where there was a split between lap 1 and lap 2 or something.
From the guy’s results*, that swim time is shocking, and certainly doesn’t point towards someone who is going to get almost 19mph average in the bike (or complete the race for that matter), and that big gap in the splits with a massive boost of speed during it does suggest he missed out some of the course. Surprised there isn’t a 2 hour or so cut-off time for the swim anyway, what is the chance that someone doing an ironman can’t swim 4k in 1.5 hours?
*given the information you’ve posted, it is pretty obvious who you’re talking about