I have a theory ( probably i won't be right)
--->Kuma goes on a rampage in Marijoa
---->Old robot went on a rampage in Marijoa 200 years ago
Kuma said to Zoro in Thriller Bark that he is a particular cyborg, different from Franky (Zoro said his material is harder than steel)
I think Vegapunk tried to replicate the ancient robot with Kuma ( Kuma accepted the experiment as we have seen in last chapters), so that's why this time Kuma attacks Marijoa, same as the ancient robot, I don't know if it's in the same time of Luffy vs Kizaru but maybe Kuma attacks Marijoa after Luffy goes in gear 5 mode ( heartbeats are the energy)
I'll wait for Kuma flashback