No, that just means the subset of genetics noisily estimated by this particular method & sample can predict those extremes (ie top 5% vs bottom 5%). They don't

No, that just means the subset of genetics noisily estimated by this particular method & sample can predict those extremes (ie top 5% vs bottom 5%). They don't report the full polygenic score in the paper that I see, although they note the SNP heritability is ~10% of variance (and I assume full heritability is a lot bigger since I do recall chronotype as being highly genetic).