I'm confident this is Allina's generic caller ID. I didn't know when they called, and didn't answer, but I wouldn't have answered anyway because I specifically asked them to communicate with me in writing. Because if you do talk to them on the phone, each time you get different facts.
Calling that number back gets you the Caller ID information mail box for Allina Hospital AND Clinic explaining that if anyone calls from that organization, this is the number that shows up on your caller ID... it goes on to say that Hospital/Clinic operators are not able to determine which extension the original call came from within the Hospital system.
Many times they don't leave a message, especially on a work phone, due to HIPPA regulations. Generally an appointment reminder but may also be used to let patients know things (i.e. your 6 month order of contacts is in).