Welllll
WC stands for Water Closet and I think Klo is short for Klosett?
The brits also call it the 'loo' which doesn't sound too far off from 'Klo' I think
So it's not actually that hard to infer what it means
To be fair I did take like 6 years of Deutsch in die Schule, aber ich habe alles vergessen + I'm not entirely sure we ever learned the word "Klo". Maybe we did.