Every AMOLED phone I've owned developed very slight ghosting of the nav bar shortly after purchase.. call it burn, retention, semi-permanent or whatever.. but it was there fairly early on.
Now, in all but the S3 I had, it really never got any worse months down the road. I remember Erica Griffin exposing that the sky was falling when the Nexus 6 she had burned in and I went in and checked mine and sure enough, if I went looking, I could see a hint of the soft buttons. But months later, pretty much the exact same level. My two year old 6P has 'burned in' nav bar bits that you only see playing the 'let's watch a full screen gray video' game. Same for the S7 and S7 Edge my wife had, etc...
A lot of these sources are chasing traffic. That's how they get paid, or at least how the sites they contribute to get paid. I always look at stories like this through that lens.