Pronouncing "th" as [t] is a normal dialect feature of Hiberno-English (English as spoken in Ireland). Most speakers here do it. It's a common type of linguistic change. Moreover, [t] in Hiberno-English is generally pronounced with the tip of the tongue behind the teeth (dental) rather than further back on the hard palate (alveolar). A dental [t] can sound a lot like a "th," which is also made at the teeth.