It is only an attack on OSS if licenses like the GPL are not respected. If copilot simply copies code it was trained on, it is more of a threat to proprietary software, since any sufficiently large copy from GPL'd software would have to be GPL licensed too.

If GPL is respected, copilot may help many proprietary softwares to be open source re-licensed. That should be seen as a positive outcome from FLOSS supporters.

But it is not easy to predict exactly what will happen and how people and companies will behave.