I agree with that. I actually suspect there is a flow issue in this case. This inside-out die off is common of dense branching corals like birdsnest and anacropora. High flow is necessary to penetrate into the dense interior or it will STN from inside-out like that.I think it depends on how you interpret the outcome. The corals in nutrient deplete studies don't seem to RTN/STN like the birdsnest in this thread. Also, I could search up many other threads that have reported similar birdsnest coral problems that have >10ppm nitrate.
While I'll stay away from the ideal nutrient level discussion, there certainly seems a difference in the way corals decline in scientific studies vs hobby, in regards to nutrient limitation.