250k/year domestic is a lot but doable. BNA-HNL is only 2 segments - it's more likely he's hitting multiple cities each week. 8 segments a week in paid F will get you 300k MQM (at least) - 500 MQM minimum * 8 = 4k MQM/week = 200k/year + 50% PAG bonus = 300k.
At 300k/year you're "only" looking at 30 years to hit 9M.
And out of BNA, if one needs to travel mostly over the SE, a lot of short hops to ATL with another short hop to SAV, JAN, TLH, RDU, CHS, etc, with the paid F bonus's it's possible to rack up the segments hardly being in the air more than an hour at a time! Plus so many of those SE cities have a ton of connection options, that he wouldn't even spend that much time in the airport.