Avast shouldn't delete anything autonomously, you should either get a notification on what is found and action to take.
What type of scan are you doing ?
Personally I don't know why you bother with this scan ?
- With a resident (on-access) scanner the need for on-demand scans is much depreciated. For the most part dormant/inert files are being scanned, the other active files are going to be scanned by the resident shields when they are activated.
So when you access the website, it and and file should be checked by the web shield and the file system shield. If you tried to run one of those files you downloaded, then that would first be scanned by the file system shield.