The coverage is done by computer. The scheduler is not really involved in legalities. That is why this item had a delayed implementation. There was a lot of programming involved.
I suspect in your case had you flown the trip you were sick on you would have had a 100 in 28 violation. It could however have been in other FAR violation. The scheduler did not really know how to explain it. The trip pickup being denied would however be correct. You can look at your block hours on your time card and add back in the sick trip and get a pretty good idea if they are right or wrong. Keep in mind however that 28 in 100 is a look forward as well as look back rule for trip awards unless you agree to a unpaid drop for a trip in the following month.