Media businesses rely on maximum readership. Losing any customers over perceived insensitivity can be grounds for termination for the offender. While I doubt the author meant it as a racist remark, I can see why ESPN decided to play it safe and fire the guy. Dumb mistake, but I've been fired for dumb mistakes in the past, too.
ESPN had every right, and good reason, to fire the poor lad. Bummer. Lesson? Do your job carefully, and when in doubt, ask.