avast has been more than "just a av" for many years, just as other tools are.
av is for a long time a misnomer.
Tools like AMS have been more than just a av for a long time.
True viruses are really rare nowadays.
Change of winning a lottery with millions of participants and only one price is much larger than getting a system infected by a virus
Scanning the wifi connection is (as you should know), part of having a decent protection/security.
If you (as you say), more than capable of determining things yourself than you should have solved the problem and avast would not tell about the risk as there would be no need for.
Change the wifi name to something that is not considered as (possibly) dangerous and avast will not mention it anymore.
AMS scans a wifi network when it is first detected.
If everything is find to be ok, it scans it every 4(?) weeks.
You can't disable the wifi scanning and there is no need for.
If you install software to help with protection only to turn it off, you might just as well not install it at all.