Lapahns are stealthy and fast! Also notable that the one hitting Kuromarimo has the facial scar indicating that it was the one Luffy helped earlier today. I guess all that blubber saved him! He is doing much better than Sanji.
This is of course payoff for Luffy's kindness, but it also symbolizes that Drum Island itself is resisting Wapol's reconquest. The former Drum military killed Wooly Hippos and many, many humans, but when nature can, it fights back! Rather than being territorial against any humans who they come across, the lapahns have learned that some humans will not bother them. This comes back way later.
This theme of nature and humanity in harmony is of course played up with the character of Chopper, but it also showed up earlier with the hiking bear! Drum already has a dangerous wild animal that gets along with its people as long as respect is paid. Now, with the lapahns, it's gaining another.
