The avast chest is a protected area (self-defence module in part), all files that are placed in there are encrypted. The only thing that can access and do anything within the chest is avast.
Yes you can see the chest using explorer and can open it, but you won't see the original file name as avast also changes that, see image. So even if some piece of malware was in the chest, nothing knows the file name of the original malware, so even if it weren't encrypted as well you couldn't really run it.
A clever virus or not, must first have a registry entry to run it or another piece of malware to run it (they can't run of their own volition), so it couldn't effectively extract it from the chest and decrypt it to enable it to be run, so files in the chest are not able to infect the host.