Why did I get items when chain fishing?

Question

Sooo I was doing some chain fishing (if anyone wants results, it broke, didn't time my press, 53 fish) and I was using a Pidgeot, Baroness. I used wing attack to kill and when it lost BP I used Twister. And it said I found some berries in the aftermath. I started to watch the background when chain fishing and it seemed when I used twister some berries fell from a tree.
And sometimes it was replaced by a mound of sand, and sometimes nothing appeared at all. Can someone tell me what's happening?

Answer 1

I found everything you need to know at Bulbapedia.

As just some background info before you click on the link, sometimes objects appear in the background during wild Pokémon battles and certain moves will cause something to happen with the object.

Comments

and chaining has nothing to do with the chances of this happening

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I've always noticed these but never had stopped and thought about why, thanks!