For the most part files won't be scanned when read, only when written (either created or modified) or eXecuted, so the file type is likely to give a clue as to as to why the file might have been scanned.
One other problem is that some applications that actually access files do so at an elevated level, e.g. when they access the file they do so with writ privileges rather than read and that in itself forces avast to scan. So I don't see how the type of access to the file that triggered the scan helps that much unless you can also identify the application accessing the file.
That was the thing that would have been very helpful when this first happened, it was suggested to use ProcMon to see what was touching these files (triggering the scan), but no one said what we should be looking for as the amount of data returned was a snow storm when looking for a snow flake.
But all in all the only thing that needed to be known was the files were repetitively which they shouldn't have been if the Transient scan was working as it should and not what the type of access that triggered the scan.
Personally I'm reluctant to see the logs get even more verbose as for your average user this isn't a benefit. Whilst having the options there wouldn't hurt, just that I'm not sure they would have helped in this particular case.
