Yes "ui" is a typical Dutch diphtong, but there are other derivations of spreken = to talk, to speak that make a better fit for the meaning given.
What about sprookje = fairy tale, or toespraak = oration?
Google mentioned that it was an Australian term. Maybe spruik is their bastardization of sprookje To my ears, Australian English has an enormous amount of diphtongs. Jacqueline BdJ