I mean I guess they could not be in network, but only one doctor in the practice accepting a huge plan in the area yet not one other doctor in the same office? It didn't seem plausible to me.
Individual doctors have an NPI number that is not the same as the practice NPI. It is not unusual in primary care practices where there are a number of providers (MD, PA, NP, MSSW, etc.) for some providers to participate in MAPD plans while others do not.
You have to research the practice AND the individual provider.
The GYN practice my wife uses does not participate in OM but one of the physicians opted in to Medicare and will see OM patients.