It causes the foal to be born with an underdeveloped colon, which is what causes a painful death within 3 days of birth if it isn't put down right away.
And yes. There is no way Abby's dam could have been a buckskin out of a black and a sorrel.
From what I've seen, most smoky blacks either look like a fading black or somewhat brown.
And yes, a single dilute (buckskin, brownskin, palomino, smoky black) will only pass on the cream gene 50% of the time because it only has one gene to pass on. A double dilute (cremello, perlino, smoky cream) will pass on the cream gene every time because it carries two copies of it.
How would you learn about new things if you don't ask questions?