It’s simply convention. Although the Straits of Mackinac are 5 miles wide at the narrowest point, in relation to the size of the lakes it makes a significant demarcation. Sort of like the Straits of Gibraltar and the Atlantic Ocean and Mediterranean Sea.

They switched to special election in 2024, so the Democratic governor would not be able to choose a senator.

The governor isn’t a health provider so HIPAA doesn’t apply to him. If he learns anything about the Senator’s condition he is free to shout it from the rooftops.
If he learns those facts from the hospital then they are on the hook for HIPAA.