The fuselage width is the same, but the cabin width is slightly different. The A330ceos do not have Airbus’s Airspace interior. The Airbus Airspace interior has more modern, sculpted side panels (see article below) that increases cabin width just a tiny bit. With the Delta One Suites already slimmed down as much as possible for the A339s, every bit of cabin width is important.

https://thedesignair.net/2016/03/24/...larger-cabins/