The post from Brad corresponds with the post from Tim in the Account Migration Beta:
Release 2.3.5 was released on May 4, 2017.
The post from the Account Migration Beta states to participate:
So with both of those posts from both ST staff members, those who created their account on or after 5/4/2017 would have a Samsung account. Yes, it was implied that this date differentiated SmartThings from Samsung accounts.
Is it possible that some people slipped through the cracks and created an ST account after that, absolutely. I know that up until a couple months ago, there was a backdoor url that would still allow you to create an ST account.
So let’s go with, the majority of people who created their accounts on or after May 4th, 2017 more than likely have a Samsung account depending on when they registered and tied in with the 2.3.5 release of the application.
When you login, if you are automatically directed to the page to enter your password and there is the Samsung logo, then you have a Samsung account.
Time to let it rest now 
The whole thing with accounts and the new app / current app has created enough chaos for a while.