The old version of ZR was very cagey when it came to how George was turned into a zombie... even with the flashback to the night of it, the exact cause was left out. That's because it wasn't important to the story. George was a zombie-- one that could talk and stuff, but he was a zombie... that's what was important, not how he became one.

In this version, George becoming a zombie has more gravitas because now his relationships with his friends and crush will be affected. So showing the why's and how's of everything makes sense.