My browsers remember my userid and passwords for many site because I allow them to do it and many time you are prompted to save/update.
Even if I come to this community my system will autofill the fields and even ask me if I want to save the credentials:
Depending on your browser you can configure many things:
If I want to sign in to BC, Facebook or email I choose to have my system remember those things so I don't have to remember them. I could also choose to have my system not remember those things and I would have to enter credentials on every site that needs them every time i visit.
Your browser will remember those things as cookies (little files that get saved) and if you go to your browser settings to clear the cache and things some will even give you an option to save stored user ids and passwords or clear them:
You can see that Chrome has my BC credentials saved as a cookie so I don't have to remember it everytime I want to login to BC:
If I go to my browsers and clear all my cache and history AND if I choose to delete cookies and stored user ids and passwords I would have to enter them again on every site I need credentials - and sometimes I do that but it is inconvenient.
So if your system was remembering things it could be because you allowed it to do so - and then if it suddenly seemed to stop it could be that your chose to clear your browser history, cache AND cookies, it could be that Kaspersky has a setting that tells it to scan and also clear your browser setting AND cookies, it could be lots of things.
Doesn't sound nefarious at the moment.