In any case, even if it WAS checked, it's poor programming on Avast's part to link a Browser install to a Program Update so that people who do have that automatic update option checked will get a browser change when expecting an Engine update only.
You sound fairly intelligent and should know that one should never assume....
As I've already pointed out, the default setting is to ask for a program update. The programming error is the user who changes settings designed to keep them safe
and then blames the company for not reading their minds.
Sorry but we've all made changes to settings and there are times, they should have been left alone.
Most of us have no problem in accepting our own mistakes. I know I've made many and don't think that will change till I'm 6 feet under.