Nah, it's not false advertising. I was going through the Samsung website yesterday to check out if I should get any new phones and that promo was available to me and ended my local time midnight. Essentially I just put the 512GB Galaxy S21U to my cart and asked me to add the Galaxy Buds Pro to my cart afterwards as well.
I didn't realize it was a one day thing but I opted not to get it since I really want the SD card slot (I have a 512GB card I don't want to let go of yet). Also, I couldn't pick it up in store apparently and don't want to deal with the trade in hassle through mail.