I think it's a mistake in the County Assessor's system. The Scott Frost buying the $345k house is a completely different person. The Scott Frost buying the $4.5m house is the former Husker. He bought that one on his own (w/o his wife) and the $5.4m house with his wife.
If you check the sale agreement for the $345k house (
https://recorder.maricopa.gov/UnOfficialDocs/pdf/20190446941.pdf) you'll see the signature on page 4 doesn't match Scott Frost's signature. Additionally, on page 1 it says Scott Frost is an unmarried man.
If you look at the sale agreement for the house he and his wife just bought recently (
https://recorder.maricopa.gov/UnOfficialDocs/pdf/20220860382.pdf) you can see the signature on page 8 matches his signature.
The sale agreement for the $4.5m house doesn't list his wife and has no signature to compare.