Avast One is a very different product from Avast Free. From what I gather in many ways a downgrade. It is in no way an update for the same software; namely Avast Free. Upgrade? Debatable. Update? Certainly not.
Popups that are designed to fool people, instead of honestly offering Avast One, are deceptive. As a user, being misled into clicking on a button, thinking it will simply update the existing software to the latest version, does not fall under changing AV's 'on purpose' in my book.
Now, the OP suggests the changeover happened without any user intervention. In that case user error cannot even be used as an excuse, even if you would redefine "user error" as "didn't catch deceptive wording and fine print". That's either a serious bug, or malice.