Verification of unlocked iPhone via iTunes

1. I bought an iPhone 7+ via eBay which seller indicates is out of contract with AT&T and is unlocked
2. A friend used the IMEI number on the phone’s box to check it’s status but the results indicate the phone is LOCKED
3. phone is currently in transit to my address (delivery after payment )
4. seller insists phone is unlocked but he did it personally via iTunes but he noticed “A NEW IMEI NUMBER WAS PROVIDED TO HIM” via iTunes
5. Seller has sent me evidence via screenshot of this “NEW IMEI” to confirm the status of phone is unlocked

• Is it true ?
• does unlocking a phone via iTunes which is out of contract generate a “new IMEI”

thanks