Good points - I'd been wondering about the same sort of factoids about this incident ... Here's a summary of what I've gleaned from the myriad news articles, etc.
The victim was not a strong swimmer (QED). Why was he so far from the bank of the pond?
It may have been a spur-of-the-moment suicide attempt. As I piece it together, he'd had some sort of altercation / argument with a fiancee at his home. According to the accounts he demanded she leave, she did, and he flounced out almost immediately thereafter.
I've seen one account that specifically stated the time lapse between his leaving the home / scene of the argument and entering the water was only on the order of 10 - 15 minutes.
Is the pond in question a common swimming venue?
He drowned in a retention pond - i.e., a pond designed to help with water (e.g., runoff) management. The pond was located in a 'park'. Such ponds are often simply dual purpose - landscaping niceties that have a functional value. Based on similar park-based retention ponds in my experience, I suspect it wasn't intended to be a swimming hole.
What was the nature of the victim's reported disability?
The most specific allusions I've found say he used a cane. He apparently had multiple 'priors' involving driving and / or traffic accident incidents, so it may be that he had a lingering / permanent physical injury. FWIW he also had priors regarding coke possession (an amount large enough to fall under the 'intent to resell' statutes) and one or more incidents involving battery (including striking uniformed EMT or police personnel). So there may have been psych / emotional issues as well.
What was the victim wearing when he drowned?
Unknown. I can't tell from the teens' video. Multiple news sources claim there was visual-only surveillance video of the scene, but I've not seen it posted online. Those that mention the surveillance video state authorities had reviewed it, and there was no indication Dunn was pushed or coerced into the water. I'd previously (cynically) wondered if there could have been a causal connection between the teens' presence and his ending up in the pond, but apparently there wasn't.
Why were the teenagers there?
All accounts that bother to address this point claim the teens were just hanging out in the park and smoking weed.