The two have absolutely no bearing, avast unpacks or sends copies of files there to be scanned, originals would be sent to the virus chest if found to be infected. On completion of the scan the contents of the avast folder should be cleared with exception to one or two administrative files AvLock.txt and perhaps one other.

If you have files in there the file name format is in this unpxxxxxx.tmp style/format. If you have lots of flies like this the most likely cause is conflict with another security based program.