There are a number of projects under the .NET Foundation umbrella, all maintained by different teams.
The .NET Foundation, supposedly for billing reasons, switched to GitHub Enterprise. People weren't aware it was happening or that a side effect of this would be that certain people would have increased access to their repos.
The person writing this post, Claire Novotny, merged in something maintainers disagreed with and that she shouldn't have had GitHub permission to merge. This lead people to realize access controls had changed and become concerned about abuse of this power.