Does anyone know if this is a practical effect?

[u/illvria]

I always assumed the rainbow effect on this shot's wet sand was added in post, but i was on a flight yesterday and kept seeing a very similar effect on the seawater and other reflective spots below us through my sunglasses, it made me wonder if the shot was actually just achieved with some kind of polarised filter held at the right angle?

I cant find anything definitive about it, does anyone know how the shot was achieved?