A lot of cruise people "hook up" and in the end it doesn't mean anything.
Now, I was on a ship when I had a girlfriend and I never fooled around on her. but when I got home I found out she had been seeing a few different guys (I never asked them how far that went). I think they just had crushes on her.
In the end, though, she ended up leaving me for another guy. Some women just have to have someone close by. If she didn't describe him as being "gay, ugly, awkward" or anything else that suggests she wouldn't go there with him, then I would be thinking about looking for another girlfriend.
But it's up to you. With girls like that chances are you will be the last to know.