A few comments... first being that the size of those "large anchors" indicates weights of a ton or more. Anchor stones had to be thrown overboard
to stop a ship... and it's gonna be a problem to get enough crewmen on a narrow boat to heft a 1 ton weight and toss it overboard.
Now... if they did... consider the impact that has on a small 20 person ship when a 1 ton weight suddenly is shifted to one side (with the help of,
say, 10 men which adds another 1,000 lbs or more) in preparation to tossing it over the side.
Now consider (if it doesn't capsize) what happens to the ship when the 1 ton weight drops off it.
Modern anchors do weigh 1,000 lbs and more. But you don't put a 1,000 lb anchor on a fishing barge or a yacht (ancient boats were not that
large.)
One reader commented that ancient anchors were used as ballast in the 1700's... and this is true... and they're found many places.
Rock isn't easily dated, so we have no evidence there. Dating carved surfaces is still harder and not excessively accurate (accurate to, I think, 100
years or so.)
The "found far from water" is another clue... the last time water rose that high was before the last ice age ... and possibly up to 1 million years
ago (from the chart duplicated on Wikipedia):
en.wikipedia.org...
I don't think they'll find much evidence (particularly since I think many of the stones have been moved).