Sorry I'm with the OP on this the Activate button is misleading/confusing, when it comes directly after a program update.
It should be clear that it is for Activating the Trial and not Activating the program update you have just installed.
This really is no different to one of the avast ads 'Activate Firewall' some may thing that 'their firewall' needs activating, not that you are talking a path to the Upgrade to a paid avast version with a firewall.