I didn't say all 7DAs were YECs. But the fact of the matter is that YEC is the church's official position. And Ben Carson is on record as believing in a six-day creation, and professing ignorance of the age of the earth. So we can quibble over the YE part, but not the C part. Ben Carson is without question a creationist.
Really? You want to hold me feet to the fire over my use of the word "hence"? Very well, let me be as excruciatingly precise as I can.
Ben Carson self-identifies as Seventh-Day Adventist (7DA). Hence, if he follows the doctrine of the church he professes to believe in, he is a YEC.
Now, it is possible for someone to self-identify as a 7DA and not be a YEC, just as it is possible for someone to self-identify as a Catholic and deny the authority of the pope, at least on some matters (e.g. all the self-identified Catholics who deny that the use of birth control is a mortal sin). But Ben Carson is clearly a creationist. He's said so on numerous occasions. Arguing over whether he is a YEC or some other flavor of creationist is really whittling at the margins. He's specifically proclaimed ignorance of the age of the earth. He uses YEC code words like "evolutionist" and "micro-evolution".
Finally, it would be exceedingly peculiar for a 7DA to not be a YEC. The name of the sect derives from their belief in Biblical literalism, and specifically from their belief in creation as described in Genesis. A 7DA who is not a creationist would be like a Mormon who thinks Joseph Smith was a con man. Again, not impossible. People can self-identify as anything they want, and once you've abandoned science and reason anything is possible. But it would be really, really weird.