Microsoft's apparent legal opinion is that training an AI on the data is the same as reading it, and doesn't require a license.
That as long as they have the right to read the data, they have the right to train an AI on it. The fact that the code is available under an open source license is irreverent to them.
As for why they didn't use their own private code to train their AI, I suspect it was more of a non-malicious: "we don't need to, this public github repo dataset is big enough for now"
Personally, I think Microsoft should double down on this legal stance. Train the AI on all their internal code. And train it on any code they have licensed from other companies too.
