The donation information comes from ProPublica. Musk's $33,900 donation is at https://projects.propublica.org/itemizer/filing/1246378/sche... .
That in turn links to the primary information at http://docquery.fec.gov/cgi-bin/forms/C00669622/1246378/sa/A... , where you can see an entry for 33900.00. (The aggregate donation is 38900.00.)
Why did you need to trust Salon.com when the official information is so readily available for verification?
Or is there something else from the piece that you are hesitant about?
As much as I generally like him, he denied being a top donor, which is not like denying any donation. He should clarify that.
Salon was pretty popular in the early days of the web. I used to read it in the mid-late 90s.