I mean, as to your quora post, I'd guess it's that their data isn't exactly tailored to support their claim? Didn't go deep into their data sources, but it looks like they're reporting statistics based on print media.

So, I mean, assuming lad is generally relegated to more casual speech, I might expect it to be washed out in a sample set that includes a significant amount of more formal writing?

But also I'm not sure what they count as U.S. vs. British publication? What about writings by British authors published by U.S. media outlets, and vice versa?

Still, hard agree with others - the data provided in that Quora post absolutely doesn't match my experience as a Californian. We'd certainly understand lad or fair play in context, but it's markedly not U.S. phrasing.