They update the data base of malware at least every 24 hours so it they placed the new version for downloading the first thing it is going to do is check for an update of it data base.
This data base you can think of as finger prints of new malwares and like the police department you are always adding fingers prints of new bad guy.
There is no real reason why they would open up the download file to add in the news updates of this database so one day or less from the time they compile the new version of AVG is going to need to get an update once you install it.
No need to be concern.