That sounds like it was caused by a sync-conflict. See: Scheduling differences between Anki desktop and Android - #4 by Danika_Dakika
If you look at the card info for one of these cards, I suspect you’ll find that it has a revlog for the study you did – which is why your collection says you studied 221 cards – but it also shows up with today as its due date – which is why it’s still due.
The only way to prevent this is to sync when you open the app and when you close/leave the app – every time. Your situation is simpler, because you only have one device to worry about. But if you start studying on AnkiWeb when you Mac isn’t in sync – or you start working on your Mac without having synced to get those reviews from AnkiWeb, you run the risk of this.
The fix that I mentioned in that other post would help you too.