Evan says that Elton John was an inspiration to him, and he admired the way he could hit high notes. He says that since he can't sing like that, he played the piano instead. The actor who plays Evan, Wilson Jermaine Heredia, played Angel, a drag queen, in both the original Broadway production and the movie adaptation Rent (2005) - he can most definitely sing "like that."
A nocturne is an original word for a musical composition, particularly classical or orchestral, that refers to or is inspired by the night.
Wilson Jermaine Heredia appears in this episode as Evan. Heredia was also in both the original cast Rent and its movie version Rent (2005). Jesse L. Martin played Heredia's love interest in the musical and previously guest starred as Ed Green in this show.