No, this only says that the about 20000 SNPs (mutations) that they can accurately measure have a limited effect on variance. What the millions of other SNPs do

No, this only says that the about 20000 SNPs (mutations) that they can accurately measure have a limited effect on variance. What the millions of other SNPs do is not known. For example there are estimates for many many thousands of SNPs that influece your height by 0.1 mm. The single variant effect is tiny but altogether it adds up a lot. Oh, and lets not forget that again this is only point mutations (SNPs). But there are also genomic insertions, deletions, larger structural variants and poly variant interactions, all of which we do not really have much idea about or even the tech available to accurately measure.