and to just highlight the OP, they had a *few* flags:
1. Not much actual flown accrual in account
2. Purchased miles
3. Using VPN
4. One-way travel on a partner, international
(5. Assuming they are NOT current Gold/75K)
6. Passenger last name not same as member
7. Passenger probably not saved in MP profile, therefore no past history.
Any combination of these triggered the review by a human. It doesn't mean just 1 will get your res cancelled.
--- as I go and look at a bunch of bookings for my airline client that orginated out of Denmark (VPN, of course) with no booking history using a credit card whose address country doesn't match the country of the traveler OR the phone number used (all 3 are different countries)