Well, yes and no, as avast has both a Persistent and Temporary cache.
Files that are scanned and digitally signed (and or) are white-listed have an entry in the persistent cache so that they aren't scanned again unless the file changes.
For other files that are scanned and show clear have an entry in the Temporary cache, so they aren't scanned multiple times if a) the file hasn't changed since the last scan or b) you reboot or c) a new virus definitions update is received.
The idea is to improve performance and cut down on unnecessary scans, so in certain cases if you scan the file a number of times or force it to be scanned, then it may be in one of the caches and it won't be scanned. It is very hard to determine if that is the case or not.
Simply changing a file name doesn't actually change the file, if you checked a files MD5 before and after renaming it, you will see they are identical and avast would see that also.