I've installed a pendant light fixture onto the preexisting plastic
ceiling box. Now I need to install another similar fixture several
feet (1'-4') away from the first. According to code, do I need a
second ceiling box or can I make an opening in the drywall and fish
Romex in the ceiling to the adjacent box for coupling?

If the latter is per code, that means I'm allowed to make a connection
using wire nuts without the connection being contained inside a
ceiling/junction box?

TIA