Nothing to worry about, those are are streaming update files in old virus definitions folders and avast is doing some housecleaning to keep the size used on the hard disk to a minimum. This just happens to have occurred between the time you started the scan and it reaching that old streaming updates folder.
If you expand the column width in the scan log you should see the location in the avast defs sub folder. Something like this C:\Program Files\AVAST Software\Avast\defs\13030900_stream and the contents of that are the .bin files, see image example.
