Discover CS told me I can't have multiple cards on the same account?

I just got a new Discover card. I've had another discover card for a few years, and I've been managing it on their app. I applied for a new card last week and got it today, then scanned the QR code to activate it. I activated the card, but then it was prompting me to set up a new account, which I didn't do. I did some googling and was trying to link the new card to my current account to no avail. Then I called discover's customer service and explained the problem, and the lady had me set up an account for the new card. I then asked how do I link my 2 cards to the same account now? She then said that I can't do that, and I'll have to have separate accounts for each card I have. I just said uhh okay that seems insane to me, and she said nothing so I hung up.

So is that actually true? I have 5 CapOne cards and I can just log into the app and manage them all from one account, same with all my other cards. I'm assuming that lady just didn't know what she was talking about? Or is Discover really that bad?