The trouble with play sand is that it's deliberately not 'sharp'. So the grains slide rather than lock. Now if you are using lost foam covered in plaster then it doesn't matter. Same with lost PLA since the plaster holds the sand away long enough.The recipe seems like a good one, and no doubt it works great. I think there is a wide variety of ingredients that will "work", and a narrower range that are really optimal. Like cooking. Depends on your local, and what raw ingredients you have easily available.
I've had decent success with play sand and ground kitty litter. It's not great, It falls in the range of "will work", but is far from optimal. I would really like to make a large batch of proper green sand once I get my big foundry completed. I'll ride the playsand batch until then.