Is the expression, “I was the admissions mistake” grammatically right?

I was drawn to the phrase “I was the admission mistake” in the following passage in the article of the Washington Post (May 2) titled, “As Ben Carson bashes Obama, many blacks see a hero’s legacy fade”.

After the speech (at Yale University), H. Wesley Phillips, 27, followed (Ben) Carson’s path and began to study neurosurgery.

“I had come from a public school in Tulsa and came from a single-parent household and thought I was the admissions mistake,” said Phillips. “But he gave me the comfort to know that if I did struggle — and I thought I would — that I wouldn’t have been the first, and there are ways to handle it. The message he gave was this backup artillery when times were hard.”

From the Washington Post.

I don’t have a problem with “I’m a dropout,” but I’m somewhat uncomfortable with the expression, “I was the admissions mistake.” A person makes a mistake, but can a person be the (admissions) mistake? Is it grammatically right?

By the way, does “the” (not "an") mean “of Yale” here? If the admissions represents for the Yale's department responsible for admission, why is it "the admissions mistake" with admission in plural form? Isn't it "the admission's mistake"?

If you Google "You were not a mistake" you will find that this usage is very common.

Logically, it should certainly be "You are not [just] the result of a mistake", but this device (a form of metonymy) is common and often carries impact because of its jarringness (though it can be carried to ridiculous extremes):

It was a proud day for her parents.

He sauntered to the local and had a quiet pint.

I was the admissions mistake [for I had only been accepted into Yale because someone in admissions had made a great blunder].

(Here, the first two examples are so institutionalised that they lack punchiness; this is appropriate for the second sentence. When an adjective (an epithet) grammatically qualifies a noun other than the person or thing it is actually describing, as in the first two examples, it is known as a transferred epithet {or hypallage}.)