What version of avast do you have avast Free/Pro/AIS/Premium ?
The free version doesn't have the functionality to 'auto update' any program, in the free version (which I use) it notifies me if there are any programs requiring update. However, If you click the button on that window, it will start the update of that program/s requiring it.
That said I believe that button may be active if you happen to hit the enter key whilst the window is open, it may well trigger the active button and consequently the program/s would be updated. I always the the X close in the top right of the window and then run the Scan for outdated software option, so I can choose what and when to update a program/s.
Only the paid versions of avast have the auto updating of monitored programs feature.