Paddy, not Patty (just in time)

[Nathan]

So here's the thing. I know it's St. Paddy's Day, but I also know a lot of male Patricks who go by "Pat" (although I only know females who go by Patsy). I don't know anyone named Patrick who goes by "Pad".

By this logic, you can understand why people who are used to seeing "Bob/Bobby" "Jim/Jimmy" "Bill/Billy" "Will/Willy" "Jen/Jenny" "Tom/Tommy" would assume "Pat/Patty". Especially if they didn't know that Patrick comes from Pàdriag. It's a simple mispelling since "Paddy" is irregular as a diminuative in that actually changes the middle consonant in the English long form of the name.