Watch people overreact about Enma reacting to the Shamisen.
Guys Enma is a cursed blade, Cursed blades are known to act on their own accord. Remember in whiskey peak, Sandai kitetsu cut fodder even though Zoro didn’t want it too. The same is happening here with Enma, Enma is reacting to the Shamisen on its own accord.
Also Cursed blades have a strange relationship with Zoro, it’s as if he can sense their emotions which is likely what is happening in this chapter.