I don't think they wanted to advertise the fact that they probably would find graves before they started. Might make some people object. Better to "find" them by accident.
You may be right, but then it would be ridiculously disingenuous to advertise that they knew there had been a graveyard there. Of course, I'm not going to give them credit for that level of reasoning. Had thie deceased been anyone but 'white' people, you can bet there would have been Hell to pay.