Don't ask me why 'cause I don't know, but people from Liverpool are referred to as "Liverpudlian"
And people from Manchester are Mancunians and people who go to Oxford University are Oxonian. I think it's based on the old Roman names for the places. Liverpool wasn't around in Roman times, so maybe it's a mock-Latin form based on substituting "puddle" for "pool." Or maybe it's a substitution for the sake of faux-Latin pronunciation, since "Liverpoolian" would be awkward. Like the way the works of George Bernard Shaw are described by the faux-Latin adjective "Shavian." (The term "Whovian" for Doctor Who
fans is no doubt based upon that pattern.)