The lawsuit is linked in the post. I didn’t read the whole thing, but skimming, the smoking gun seems to be that an implementation of Splunk’s S2S protocol was posted to his personal GitHub while he was still an employee. They claim that the header files just had the Splunk copyright notices removed, but just being a re-implementation of the objects wouldn’t surprise me. Depending on the jurisdiction that might matter.

There are also various copyright claims on things in manuals, plus claims that they infringed numerous patents.

All in all, it sounds pretty bad, but lawsuits almost always do. I would wait to read the responses before coming to any conclusions.