I was very confused because I had implemented a bad word filter which I knew worked (it was the most interesting part of building a word search). And obviously, I didn't hard code that string in my program!
I asked to see the offending puzzle. Upon inspection, I found that the word search contained the word "ORIGINAL". When reversed for the word search it is "LANIGIRO" (which contains the substring "NIGIRO"). The start of another word - "LAW" - was placed next to "LANIGIRO" (by random chance) creating the string "LLANIGIRO". The two preceding randomly chosen letters were "K" and "I", forming the string "KILLANIGIRO".
I explained it to the superintendent, and all was well again.