If you happened to be downloading a zip/compressed file that would be unpacked in this temporary _Avast_ location, so the total size could be very large. That said 463GB is absolutely massive even if it happened to be an archive file.
As an Avast user, I'm at a loss as to what it might be, it certainly isn't normal and I personally haven't come across it on my installations nor seen an instance like this (to my knowledge) in the forums.