Interesting, I think Holland may have some discrepancies in what they are telling folks. A cut/paste of their 2018 "What you need to know" pdf (downloadable from their website):

CLOTHING Most evenings smart casual attire is appropriate. Shorts, pool/ beachwear, distressed jeans and men’s tank tops are best left to the daytime and are not permitted in fine dining restaurants.

Gala Nights evoke the grand traditions of cruising as guests dress to impress for special events on board, including a five-course gourmet dinner in the Dining Room. For gentlemen, collared shirt and slacks are required in all fine dining restaurants . For ladies, dressy attire is appropriate, dresses skirts and slacks are all acceptable