OMG. That looks dangerous... ...but apparently... it's not that bad. Apparently Piranhas are not likely to attack humans unless they are hungry or desperate (e.g. when trapped in a pool or water separated from the river which is drying up). Apparently the dry season is the worst time because of lack of food. Fishing for piranas like this and slipping into the water is not my idea of a great way to test it.
I'm also pretty sure that piranas don't strip flesh "in seconds" as shown in cartoons or the movies, so even in the event of a piranha attack there would be time to get pulled out, again I'm happy to leave that as a theory!
One thing is certain though, I certainly wouldn't go fishing for Piranas like they do in Brazil: