Thanks for reporting this issue, and welcome to the forum. I can confirm that this behavior exists (I just tested it with my own account) and I think I have an explanation.
If I remember correctly, in the beginning players would inadvertantly mark *all* of their cards as unfamiliar. Then they could not start a game, because the game could not find 10 cards they were familiar with.
The solution was that 10 cards from the base set were always marked as familiar, I think it is one of the 'suggested Kingdoms' from the rulebook of the base set. This is what you are seeing.
What can you do about it? I assume you want to play games that do no contain cards from the base set. If you want to play a bot, go to the "New Table" tab, then press the "Create Table" button. There, press "Select Kingdom Cards", which shows you the page I appended as a screenshot. Here you can choose a card directly to include into your Kingdom, if you so desire. Any card not explicitely set will be taken at random from any of the selected sets to the left. What you need to do is to unselect the base set. Klick on the tickmark I circled. It should become empty, and this means only cards from the other sets will be used.