I'm curious what would happen if they looked at, as separate categories, people who mastered out of a doctoral program, people who did the 5-year BS/MS, and people who obtained a doctoral degree as well as a master's.
My guess is that pure MS would correlate positively from CS programs that require a background in more advanced math and algorithms. Info sys degrees typically don't.
I'm not knocking those degrees, keep in mind we're measuring performance on a technical interview, which often leans very heavily toward algorithms, trees, sometimes graphs, and occasionally numerical analysis or computing.
If the MS degree data includes a lot of programs that dont include this background, then this woukd not be a surprising result.