That it did well on held-back data should convince you that you don't understand overfitting.
They didn't do well on the gene level: Analyses of individual SNPs and genes did not result in any replicable genome-wide significant association
No, they didn't try to measure non-linear effects. Nor did they try to measure environment. That is all irrelevant to measuring linear effects, which was the main thing I wanted to convey.
No, the fact that you can calculate a linear model that predicts h_2 in a way that fits 0.4 or 0.5 of the variance doesn't mean that the underlying reality is structured in a way that gene's have linear effects.
To make a causal statement that genes work in a linear way the summarize statistic of is not enough.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.