Question Is my "new" phone really factory unlocked?

[rogue55]

I just bought a "factory unlocked" galaxy note 8 on ebay. Was supposed to be new and looks like it was "open box" new, which is fine. however, as soon as I started it up, I had a T-Mobile splash screen. I'm thinking this is a dead give away that it is not unlocked. But I have no experience in this subject. Any pointers? My plan is to replace a 6 year old LG Optimus on my AT&T network. Should I return this?

 

[Nealnyethebadguy]

Dont return it yet sometimes carriers will unlock phones after contract infact my unlocked s3 says att yet i use it on tmobile before return put your simcard in and see if it lock up source- my 12 year old brain