If I recall, at the time, Avast bundled their SafePrice with Online Security (extension). This was the same service Avira used for their Price Comparison, which is currently included in Avira Browser Safety.Yes I've read this blog about avira BS too. I don't know what kind of suspicious request he was looking for with fiddler, but, to do its job, Avira need to know the domain you are requesting.
Related Article by HTG: Avast Antivirus Was Spying On You with Adware (Until This Week)
Avast's Response: Avast Antivirus Was Spying On You with Adware (Until This Week)