It does make sense! So healthy or not, any large amount of ingested sand will NOT pass through a tortoise or turtle? The biggest mind boggle to me was that they said a healthy tortoise will not become impacted.
This is not so absolute. Some sand MIGHT pass through any tortoise, healthy or not. Conversely sand can get stuck in the gut of any tortoise, healthy or not, and build up over time.
No one knows why it sometimes can be passed through and why it sometimes gets stuck. No one can say that a tortoise who passed some sand in the past, will still pass it today.
I find in these situations it sometimes helps to consider the source of info. What have they experienced? How many tortoises have they raised and kept? What sort of experience do they have to base their assertions on?