From the article I read it didn't say employee was attacking them hours every day. From the articles the employee posted a message on an internal slack "Outrage Notification" channel which looks to be an internal venting channel containing similar content.

Atlassian has values "Open company, no bullshit" which they selectively use. "Open company, no bullshit" until it isn't. Example, this case, upsetting Mikes ego.

I was on a team at Atlassian that got constructively dissambled after not being happy with some changes for the worse. Worst retro I've ever been in, all developers heads on desks, manager: "suggest how we fix this issue", developers silent as every answer from the developer got the reply from manager on the lines of "no, you know we can't do that anymore". Then the digging through historic slack messages and social media posts started followed by departures...

That was a very long time ago now, seems not much has changed.