Sounds like a messed up situation, based on their retelling of events. Glad they got the attention of Spencer - hopefully something can be done to improve things at Mixer, because it sounds like there was a breakdown.
When you run a division with tens of thousands of employees, you rely on a reporting structure. When there's a breakdown in that structure, or when a manager isn't abiding by the policies set out by the overall corporation, they need to be held accountable. And judging by Spencer himself now getting directly involved, despite this probably occurring several managerial "levels" below him, I suspect shit is going to fly.
I'm not going to be overly cavalier with other peoples' jobs and say that Microsoft need to "clear house" at Mixer or whatever, but there clearly needs to be an internal review of, at minimum, why Mixer's HR came to the absurd conclusion it did. As for the manager, I suspect they are probably 72 hours or less from looking for a new career.