The complaint submitted to the court presumably has more details. It would have been nice if the blog post had included a link to it directly, but they did include the case identifier.

Edit: I went ahead and dug the information up. Here are the details about the court case on PACER (requires login): https://ecf.cand.uscourts.gov/cgi-bin/iquery.pl?924893974295...

This appears to be a link to the specific complaint: https://ecf.cand.uscourts.gov/doc1/035018374190 (20 pages, ~1 MB)

Edit: I've uploaded the complaint to the RECAP archive, which I believe you can access for free as a PDF here: https://www.courtlistener.com/docket/16154366/elasticsearch-... (see document #1)

One of the claims that's easy to summarize is that Elastic alleges that floragunn made massive changes to its codebase shortly after Elastic released proprietary updates, contrary to floragunn's typical development practices, and that these changes included copies of Elastic's proprietary code:

> On June 7, 2018, just over one month after Elastic made the source code for XPack version 6.2.x publicly available under the Elastic License, floragunn made a sudden and very large change to the Search Guard code. This change comprised 244 additions and 145 deletions of code. Many of these changes involved the wholesale copying of the X-Pack code that Elastic opened little over a month before.

The complaint goes into more detail with specific alleged examples of source code copying, showing the code in Elastic's codebase and the corresponding code in floragunn's.