I followed up on this and had some conversation with one of the Skywalking PMC members.

They escalated the situation to the company legal of Byte Dance (the parent company of Volcengine Inc.). Then Volcengine has added an Apache license file for Skywalking. Skywalking is open-source software, it has no commercial license. So nobody knew how to evaluate the impact of this violation. And some people thought it was well resolved.

I felt very frustrated about this. It means there is totally *zero* risk to violating an open-source software.