Usually hair balls are left in places easier to find. The back of the refrigerator was a surprise even though Lancelot, one of my older cats, does go back there sometimes to sleep, and all the cats climb on top the refrigerator. They like high places.
It reminded me of an embarrassing hairball moment from a few years back. When I went to a faculty meeting. I sat at a table with half a dozen other college instructors. I reached in my purse to pull out a pen. Instead I pulled out a hairball.
Hairballs happen. Nowadays I make sure my purse is zipped shut when I am at home, and I glance at the insides before I leave