Unfortunately yes it's legit, alot of s8 and s9 owners have been hit with the screen burn issues, if there is the slightest thing wrong with the screen they pull you on it the s8 & s9 suffer screen burn very easily, thankfully s10 onwards it doesn't seem to happen much or its much harder to burn
I had the same message to the t from them when traded in my s7 edge that was in perfect condition. So i called samsung customer care who said they would contact the trade in group. Then sent the samsung references number from the call to the trade in company. Got a message a week later to say the trade in was complete