No I don't believe it simulates a zero day attack as you have disabled an integral part of the 'overall protection'.
The file system shield does more than just a cursory scan (and you are killing that) weakening the collective protection of Avast. There is the Hardened Mode, files are automatically sent to the Threat Labs, whilst they aren't directly under the heading of the File Shield, I believe it triggers these in the case of unsigned executables, etc.
By disabling the file shield at the very least you allowing malware to get a toehold.