If I remember correctly this came out of a study that tried to recreate dinosaur vocalizations as accurately as possible. They looked at skull shapes and by looking at birds and other animals tried to approximate how and where sounds would reverberate. Or something like that. There are YouTube videos of all the different species and they explain the process a lot better than I did. There's obviously a lot of guess work involved and it's probably only vaguely close, but still cool!

Psh don’t be ridiculous. Obviously they cloned one and recorded it.

I have no background in biology or paleontology, I just watch a lot of dinosaur centric YouTube channels; so take this for what it is. I believe the most current understanding is that T-Rex wasn't feathered but did have quills or "proto feathers" around the head area. So this might still be inaccurate visually, but I believe the focus was on the auditory :)