What are your sensitivity settings? That area is very small so it would not take much to surpass the sensitivity threshold once the pir detects something. How much movement does the bush do? The two boxes of your detection zone have bush leaves which I am guess move fairly often.
Once the pir wakes the camera up and it starts recording, the second pass is the sensitivity settings and detection zone. If the frame passes those the clip is saved and uploaded.
I think you’re right about the pixel sensitivity! Keeping it at 100 seems to trigger detection almost no matter what (I wonder if it has anything to do with image compression noise).