They were so eager to make the lemon+cello=limoncello pun that they just grabbed the nearest kid's cello. They didn't even bother to take off the tape that shows beginners where to place their fingers. Maybe they meant to playfully undermine the "sophisticated" angle, but it doesn't feel intentional

Or maybe it was Danny's own cello, and he was teaching himself to play! After mastering the arts of acting, directing, and liquor production, he needed a new challenge--a stringed instrument!