The dock hand makes a comment that with one of Jaskier's songs "it took me to the fourth verse to realize there were three different timelines" this is a joke about the first season of the show.
For Feainnewedd, the blossom that sprouts wherever Elder blood has been spilled, the series uses the African violet, aka Saintpaulia ionantha.
Fans of the games with a strong ear may recognize the guard at the docks in this episode, as he was the voice of the underworld dwarf, Cleaver, as well as various other NPCs in the The Witcher 3: Wild Hunt (2015).