I know this is naive but it takes a village. Young people often push the bounds of safety... and it's up to adults to protect then until, as we say, their brains come in. Duty of care that I like to think we all share.
I wish he'd walked away. Reported them. For drinking, for harassing...
He was looking for a phone. He did have a snorkel. He may have said he was looking for a girl's [phone] and the over all impression looked bad. Underwater upskirt.
But there must be rules on the river. Unspoken etiquette. Leave other tubers alone.
Grown adults get involved in stupid skirmishes all the time. Sporting events, open roads, bar fights.
These were children. You can't expect to engage them as adult. Add alcohol, add lack of life experiences, add inherent invincibility and it's -- well, IMO, the only interaction with then if there is one is to report them. For their own safety. Losing you 'tude as an adult over taunts from children, that's a tripwire.
You gotta know when to stand down. Same for the teens but they're teens for a reason.
We expect more from the adults. We need to. Walk away, drive away, take your lumps if you need to. They were children.
JMO