Rubadub
Absolutely not a fair comparison with fire service or police as the examples you site are presumably within their juridstriction. Would I be happy if my local fire service went 70 miles away to help rescue a man who had set off a load of fireworks in his house leaving us with no cover?
If someone has been told that their primary job is the safety of a particular group of people - in this case the people swimming in the safe part of the beach - then that responsibility comes before all else. Just out of interest, if someone had died in the safe part of the water whilst he was with this man then who would have been responsible? Or would it have just been one of those things? Because if it was one of my family you bet I would look to prosecute both the idiot who went swimming in the area marked as being unsafe and the lifeguard for deriliction of duty. Duty and responsibility is a bitch sometimes but if you are unable to make those calls when they come then don't take the job.
The criticism I would have of the company is why they did not have at least two lifeguards on. I thought that would be standard practice.