Re: Curiouser and Curiouser
As Pascal says, he moved company. You may have to read between the lines, but it's fairly clear in the article.
After inventing the "thing", he assigned the patent to Cisco - fairly common that employers want the patents on things their employees invent as part of their employment. So Cisco, not he, owns the patent.
After that, he left and (with other Cisco employees) startup up another networking gear company - Arista. Now it stands to reason that some of the things they'd like to sell would infringe said patent, so they have three options : 1) Say "pretty please" to Cisco and buy a licence on whatever terms Cisco may (or may not) want to give them; 2) avoid infringing on the patent (which may mean leaving features out of the product); or 3) challenge the validity of the patent. Don't forget that other than in the case of a standards required patent (ie something that's incorporated into a standard*), Cisco do not have to licence the invention if they don't want to - they can refuse and so prevent any other vendor from taking advantage of the invention. And if they do licence it, they can name their own terms - which could be quite expensive.
So here, it was Arista that challenged the patent, and presumably this happened before Cheriton left. But either way, strictly speaking, it's not the inventor challenging the patent, it's his company.
* Where a patented method is incorporated into a standard, there's normally a FRAND clause attached - the holder of the patent must licence it to anyone on a Fair, Reasonable, And Non-Discriminatory basis. This is to avoid someone getting their patented method included in a standard, and then being able to to hold everyone else to ransom - or even block certain competitors from using it at all.