The country's economy is unstable, the result of a stock

[AnupamJ167]

"The country's economy is unstable, the result of a stock market crash that occurred ten years ago."

Above is a sentence from the Manhattan GMAT Sentence Correction book. According to the book, the sentence is correct.

However I have two doubts:
1. We are talking about a specific stock market crash that occured ten years ago - hence should we not use "the" instead of "a"?
2. Are we not skipping "as a" in the original sentence to connect the two clauses? Does skipping this connector not result in a run-on sentence?

According to me, the correct sentence should read as follows:

The country's economy is unstable as a result of the stock market crash that occurred ten years ago.