This is a randomized trial with hundreds of subjects. The two groups should be statistically similar to each other in their magnesium levels (and other attributes). That's the purpose of randomization: so you don't have to find and control for confounders afterwards like you do in a non-randomized trial. It's easy to obscure or reverse a result by controlling for the wrong variables, for some examples see https://slatestarcodex.com/2019/06/24/you-need-more-confound...
On closer, look it is a randomized trial with 3 hundreds of fat, hypertense patients, most of which are on some kind of drug or platelet treatment. That 70% hypertense bit pointing towards most of them being magnesium deficient to begin with.
The quantities involved are so small that they might as well not have bothered. In Asia, people have consumed +10mg of K2 for extended periods of time.
720 µg MK-7 plus 25 µg vitamin D or matching placebo for 24 months are laughably small. So small one can only wonder if they were trying the homeopathy where they keep diluting some concoction and claim it still has some effect.
Not even getting into the issue of whether D supplements are an adequate replacement from sunlight.
