"Bounced": a family disaster

This image and its accompanying handwritten text intrigues me in Fishguard's  Ein Hanes/Our History collection.  (Unfortunately there is no record of who wrote  or donated the item.)

The photograph, reproduced in the county magazine (but no date for either),  is titled 'Telegram Boys in Fishguard making asses of themselves'. It shows three lads in postal workers' uniforms  fooling around with a donkey, perhaps in the 1920 or 30s. At the back someone has written:
Henry Harries (R.H.S.)
Brother of William, Mary, Ellen and Jan. Had an accident being  'bounced' by a sister which left him permanently deformed. He couldnt stand straight, worked as a postal worker. This photo at the P.O.... He lived in a one room cottage by the blacksmiths in Dinas.
(I presume Henry is the young man on the right standing with a hunched posture beside the donkey's  head.) 

I find this story inexpressibly sad. The 'bouncing', presumably by a sister  who was herself a child,  must have damaged the baby's neck or spine in a way that was at the time irreversible  and devasted the rest of his life (and presumably hers too.)  Poor Henry - he did have a job but not, it seems,  a wife or companion. Was he lonely and isolated as a result of his disability? Let's hope the family supported him. The fact that someone has taken the trouble to record his story suggests he was not forgotten.

And RHS?* The only association I make with that is Royal Horticultural Society. Perhaps he was a champion gardener?  I will make it my duty to find out more about this little hidden history.

*Talpa has suggested it could be an abbreviation for Right Hand Side (of the photo).