It may well have been 'the right kind of rice', I'm not sure. The mushrooms were definitely not cooked with the rice, they were separate and not mixed in at all. That was what most surprised me.
I also expected more ingredients, although I'm not sure what. Perhaps some onion?
Anyway, your point about the 20 minutes makes it clear. I doubt there are many pub kitchens that can watch something cooking for that long!