New zombies get made when people die. There is also a kind of “magical” element to these zombies (and many zombies in movies / TV shows where the zombie bodies live on even though they wouldn’t in real life).
The new zombies thing doesn’t work because I have seen zombies in suits or apocalypse inapporiate attire. That means they’re zombies from season one. Therefore, either the zombie virus prevents decomposition or it’s supernatural.
Was it Dwight?