He could have mentioned it, but I don't understand why you think it's important?

The authors of the actual scientific study are Richard Border and his co-authors. Scott Alexander is just a well-known blogger who gets credit for writing about it in a vivid way that got people's attention. He's not a primary source, so for the purposes of this article, it doesn't really matter whether he's using an alias or even whether he's a psychiatrist. (It's not a credential in the relevant field anyway.) You can verify the quotes by following the link.

Calling up other scientists in the field and asking questions about a scientific paper is how science writers verify a science article, and Ed Yong did that.

> I don't understand why you think it's important?

Scott Alexander is a pseudoynm. Journalists referencing that name should note this, along with the fact that his credentials as a psychiatrist are not publicly verifiable.