Is this file present:
C:\ProgramData\AVAST Software\Avast\report\Viruses & Malware.txt
If I remember correctly this is the report file for the Smart Scan, but I don't know if this report is created by default or if you have to tell it to create it.
Whilst you may have asked for the files to be sent to the virus chest, I don't know if there would be circumstances where rootkit files couldn't be sent to the virus chest. Then it would be down to the options/actions you have set up if the first option/action can't be carried out. Plus to get ride of rootkit files, I just wonder if Avast wouldn't require a restart to remove them. Also, if memory serves me well Avast does an anti-rootkit scan 8 minutes after boot and presumably nothing was found.
That said 61 rootkit files would seem excessive.