My opinion would be that the a fib people are taking calcium with the d3 supplementation. Most Americans probably have too much calcium in their diets before any supplementation of calcium. It may be possible to upload too calcium with the assistance of d3.
The whole article only mentions Vit. D. Yes, one can get too much by taking plain Vit. D. But vit.D3 is a different thing. I’m not sure what is different about it, but I have read that it’s nearly impossible to get too much with the D3. I take 2500 a day and do not get colds.