That's odd indeed. I have a different 2FA seed for my retail and AWS account, but I've never tried using the wrong one but it's conceivably they allow you to use either
I wasn't able to use either though, as I said above. My retail 2FA TOTP failed for my retail account, but my AWS 2FA TOTP worked for my retail account (and for my AWS account).
So something shady is going on.
Well what's even more odd is that sometimes they do and sometimes they don't.