It happens. Lots of people crowded in a small space. Unfortunate.
Admiral and I have been on about a dozen cruises and one ship had a similar outbreak (and the Admiral was unfortunately one of the unfortunate, I dodged it). Not fun when that happens. Otherwise the food, drinks, casino, visiting ports and generally doing "nothing" on sea days are great. Many say you either love cruises or hate them. Put us in the former category, one has to get out of Michigan in the winter! Caribbean cruises have been a "go to" for us.
What a shame. The recent Celebrity cruise we did, would not let anyone serve any food to themselve in the buffets until the ship had been at sea for 48 hours to see if anyone fell ill in those first two days as a precaution. We have done about 20+ cruises and never had any issues but can imagine it's not too nice if you do have.