Looks about like my iPad view with fresh download of area using Navionics charting. On the zoom level where the lighthouse shows, it says:

"[FL{3) 30S 12M] White flashing light with a period of 30 seconds and a range of 12 miles."

I have the seen the track of the race boat as it approached and struck the reef. Can't find it now. Even if the light was functioning, I think their track might have put them more than 12 miles from the light. So the light would have been away from their course and could have been seen as another vessel, not a threat. As someone mentioned, if they saw the lighthouse charted at any zoom level, that should have been taken as a cause for concern.

I think the rough rendering of the shoals on the iPad is due to the poor Navionics charting data quality in that area. The charting around Mauritius is much crisper and shows at much wider zooms.