Paint The Town Red?

[LockerOfWecs]

First time I loaded the game I got this achievement. Didn't even kill any zombies yet, and bam, achievement. I don't think I was supposed to do that.
http://steamcommunity.com/id/Weclock/stats/BurnZombieBurn
See the evidence.

[Fangoram]

I just had the same thing happen to me except I've had the game for a few days and today when I started a game "bam" paint the town red.

[chrs3]

with me it unlocked while killing zombies.

[caddux]

After I killed a few zombies BAM I got this too! :D

[NowImNothing]

I got this one in tutorial #3.

Before it started.