I applied and was approved immediately. I will await a formal and direct notification to me as to what will happen.

I documented the offer by keeping the email and capturing the web site as an MHT file. I have that if this turns into something bigger.

I presume they will just rescind the offer and give you the option to cancel the card since it doesn't cost you anything to cancel. I guess the only impact is a slight effect on your credit score?

There are numerous precedents for rescinding offers made in error (but usually they need to be blatantly and obviously in error....)