You formatted the error message as code using the
<pre> HTML tag,
he formatted it as blockquote using the Markdown
> syntax and corrected a capitalization mistake.
Whether this error message should now have been formatted as code or quote is in this case pretty unimportant and would be another discussion. I would consider both options equal.
However, it's strongly recommended to prefer Markdown syntax over HTML tags wherever possible, so also to format the line as code, you should indent it with 4 spaces (Markdown syntax), which will then internally be converted and displayed on the site using the HTML tags
He however did not only do this minor formatting improvement, but another necessary spelling/grammar correction as well.
After having summarized the difference between those two edits, we can conclude that the second edit is indeed better and follows the formatting guidelines, but in my opinion it is not too different from yours, especially as your intention was not wrong, so i would not have rejected and replaced the first edit, but improved it.
As he said in the comments to terdon's other answer, it was an accident and he wanted to click the "Improve edit" button instead of "Reject and edit". So except that you now learned how to better format posts, you should not worry about this. :-)