I don't see a problem with this. Being a puffed rice product, there's no way they can guarantee volume, hence the "about", even if it is far less.

So long as there are 15 servings at 36g each, that's all that really matters.

I'm not really sure why they even bothered with combating the volume estimate in the first place. Even ultra fine particle sized products like flour, it's still recommended to measure by weight for recipes simply due to volume being a poor accuracy measure.

Now, if the box was short in ounces, then they'd have something.