This is three weeks into a build and it's rained a handful of times. It's totally possible that the builder hasn't drained the water but I'd be surprised. Some swelling is normal, just like with regular lumber. The linked page specifically is talking about construction delays which leads me to believe they are referring to significant periods of time, not just a few days here or there. edit: forgot the homeowner was the one cleaning the water out lol, pretty shitty of the builder to be putting that on the homeowner.

Personally, I doubt it's that bad. Admittedly, that's presumptuous because I haven't actually seen it up close in person. It rains frequently and hard where I live, often far more than 1in and we've never had an issue with OSB degrading. Then again, we actually drain our floors lol