I wonder what hardware configuration that other person was running.
I’ve not seen anything like that in Safari on my MacBook. (Older than yours, if I recall correctly).
That video looks like a video card driver problem, something in the refresh during the scrolling operation. Have they changed the video subsystem since the introduction of the MacBook?
My config for the graphics:
Chipset Model: GMA 950
VRAM (Total): 64 MB of shared system memory
Vendor: Intel (0x8086)
Device ID: 0x27a2
Revision ID: 0x0003