Simple, as I said the folder is a physical location when viewed in windows explorer and is treated in the same way as all other folders when using the context menu right click scan. You are asking Avast to scan it, so it does as you ask. And it uses ashQuick.exe to do that.
Why would you even be doing a manual scan on the recycle folder, just periodically empty it.
It makes sense to right-click a file (to scan for viruses) when it is initially downloaded and placed in a folder.
Why would you need to scan a file when it is initially downloaded ?
Given that Avast on-access scanner does just that, scans newly created, modified.