I have no expertise in this field and this is what I got just from reading the article without doing any further research.

It seems that a consortium of giant tech companies got together to make a royalty-free video codec called AV1. This included getting legal agreements from a bunch of relevant patent holders that they wouldn't pursue legal action against anyone implementing AV1.

However, due to the U.S. patent office's current policy of issuing patents left and right and letting applicants sort out whether or not their patents are actually unique in court later, lawyers representing Dolby and a couple of other companies that hold some separate video-related patents have smelled money in the water and are trying to sort out whether or not their patents are unique in court.