Health insurance

My health insurance is showing that one of my doctor’s appointments was denied because it was out of network. I called the doctor and asked if they were in network with my insurance and she kept saying “yes we accept that insurance”, so is “in network” the same as “accepting the insurance”? I didn’t ask her too many more questions because she seemed like she didn’t know too much about it. When I had my appointment, they did accept my insurance and I had to pay a $10 copay for urgent care. So if it was out of network, wouldn’t I have known?