It's extremes as usual - the situation described in the OP is ridiculous for a 2 hour play session and inappropriate, but it doesn't then follow to the other extreme that no children require snacks and that those that do are trained into wanting them.
All children are different, as are adults. It's great if you can manage feeling hungry, but I can't. I never snacked as a child, used to have to wait hours between meals, used to have a lot of tearful meltdowns where I just couldn't cope. It got worse during adolescence. If I go too long without food I get dizzy, clumsy, get the beginnings of a migraine and feel nauseous. I'm not diabetic, neither am I overweight, but I am extremely affected by blood sugar dips, especially when hormonal. It is different than just feeling hungry, sometimes I don't even notice that's what it is and it takes my dh noticing that I am irritable and bringing cheese and crackers.
So I can imagine it might be the same for some small children. Not all, but some. My niece for example would go a whole day without bothering to ask for food, and can eat whenever, my dcs both need three meals at regular times with a little something at the mid way point or they would be distressed. Not whiny, not cross, not demanding. But upset and uncomfortable.
In that soft play situation, my dcs would manage for the 2 hours without a food break, but would have something before going home, with dinner another 11/2 to 2 hours away. It won't make them obese gluttons! Yes, you don't force food when they're not hungry, but on the flip side you shouldn't withhold it unnecessarily when they are.
As long as lots of exercise is going on, and the snacks are of a reasonably healthy nature, it's really fine.