I was under the impression that MSP airport uses the Hennepin EAST sub-system as their "Home" system. One of the sites for that sub-system is located at Fort Snelling right next to the airport.
The way this ARMER system works is that there are many local sub-systems that cover a relatively small area. If users roam from their local/home area, they "may" affiliate with adjacent sub-systems to link back to the "home" system. So if MSP was heard on Hennepin WEST it could be due to a user roaming in the area of that sub-system. Once the unit departs the area, then the traffic for the MSP talkgroup ceases.
The ARMER system is a pretty complex system. I'd think hearing airport talkgroups in Wright County might be pushing it.