In the TKI website, the Ministry of Education says: 

"UDL is an overarching approach focused on the inclusive design of the whole learning environment at the outset. UDL aims to ensure all students have full access to everything in the classroom, regardless of their needs and abilities. Students are supported to selfdirect learning and monitor progress."

"Differentiation is a strategy aimed at addressing each student’s individual levels of readiness, interest, and learning profiles. The teacher modifies content and processes to address the needs of each student. The teacher directs students to specific activities to further their learning."

https://inclusive.tki.org.nz/guides/universal-design-for-learning/udl-and-differentiation-and-how-they-are-connected/