https://www.countrylife.co.uk/out-and-about/dogs/curious-questions-can-swan-really-break-arm-190943

The good news is that you can rest easy. Birds that still retain the power of flight are essentially built for lightness rather than solidity, and while a swan can whip up fantastic wing tip speed its bones are too light for there to be any serious heft behind their blows.

'It’s a myth that they will break your leg or arm with their wings,’ John Huston of the Abbotsbury Swannery in Dorset told the BBC a few years ago. ‘They are not that strong and it’s mostly show and bluster.’