Rust stains from a poorly sealed iron keel are not unusual. Though I can't say I've heard that particular "wasting" term, I'd expect the surveyor was concerned about corrosion and loss of material of the keel bolts themselves. A proper fix/check would probably involve dropping the keel - a fairly major operation obviously.
The keelbolts ought to be SS, so the rust itself is likely coming from the iron keel. Whether you could "pull one keelbolt at a time" will depend on how they were installed in the keel in the first place (ie, drilled and tapped, or cast in place)
If your insurance company takes the surveyor at his/her word, this could be an expensive recommendation.
btw - you probably should have started your own thread for this.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"