A coup wouldn't have him immediately fired. Instead he'd be placed in some advisory position while they transition in a new CEO. The immediate firing means scandal of some sort.

No. A weak coup would do exactly that. They have to isolate and alienate or they risk the ousted leader coming back or damaging the company.

How do these board members relate to Microsoft's holdings? Is Microsoft making a play here?

Honestly have no idea, but I'm sure a shift of control could cause this.