It is clearly Zoro's own Haki (said in multiple vivre cards, databooks, road to laughtale 4-5 times already).
Regarding the Shamisen, no it did not react to Hiyori's Shamisen. It was a simple red herring at the end of ch. 1032 which was cleared up in the very first page of ch. 1033.
Zoro listens to Hiyori's shamisen -> loses focus -> Enma goes wild -> he gets it back under control = [
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It still doesn't change the fact that Zoro was causing more damage to more durable characters with CoA alone than Yamato managed with CoC.