The only think I can even remotley think he's talking about is in the scouring it says Sharkey's Ruffian's were mistreating hobbits, to take that to mean SA without additional implications is a huge stretch, assuming he's talking about the books??
Or at my most generous, maybe by IRL he means Tolkien's WWI experience, though he never mentioned SA in his letters it did happen
Ah now I remeber who this guy is