Github's TOS already contains highly questionable language about a "license grant to us". I removed my code from Github when they added that, because I have no interest in risking giving Microsoft additional licenses to my software beyond those I give everyone.
The $5k matching would not even pay for a lawyer's time to review the current TOS and determine if that language in it actually does grant them an additional license.
MS playing nice with open source starts to smell a bit like an attempt to ensnare and trap developers in an MS ecosystem. But this time around it is not about Windows as a target platform, but about dependencies on tools (VSCode), libraries (.NET Standard) and services (Github, Azure) provided by them.