Ooooohh, yeah I heard him mention using the robots weapons against them, but for some reason I just thought they were weapons used by other unseen human enemies lol.
And it was this wall right behind the tents at the far end, just before you platform over the fence with the cake boy.
It looked like it was being prompted to being shot, the texture wasn't quite lined up right, and it was jutting out enough that I was even able to stand on it lol.
Plus it said 0% secrets at the end screen so I assumed I missed it.
I look forward to the next 3 levels!