Reading the article, something about this sounds shady. If I'm understanding correctly, Kevin's "endorsement" seems more like a review, not unlike one you'd leave on Yelp or Google. I get the station outlines how it's a violation, but it seems odd to end contract negotiations over this.
Having heard stories from former colleagues who work(ed) with what's now Tegna, part of me thinks either the station or Tegna wanted a reason to not renew his contract, and found a loophole. I guess time will tell.