You're right that it wasn't his profession by choice - it was decided by his relatives that sending him to HMS Conway would be a good way of finishing his education and providing him with a career. His closest living relative has expressed the opinion that, even if he had not been involved in the Titanic sinking, he would not have remained at sea.
In this context, it's quite moving to read some comments he made in a reflective mood a couple of years before the Titanic sinking. He was much happier in the steamers, and commented that he had never felt so happy at sea before.
By the beginning of 1912, he was looking forward to that summer on the Atlantic run.
Alyson, they were just teasing him as the only boy among so many females (which included his cousins, aunts and grandmother) - they dubbed him "Puck among the roses." The "roses" being themselves, of course, and "Puck" is a nature spirit, most famously used by Shakespeare in "A Midsummer Night's Dream". Originally sometimes a rather sinister figure, "Puck" over time came to be considered more playful and mischievous. To be "puckish" now means to be impish and whimsical.
Rudyard Kipling (a distant relative of the Moodys) published "Puck of Pook's Hill" in 1906, which suggests the word and character might have been popular in the early years of last century (the incident with Moody took place around 1900).