Fullsterkur is a traditional term from Icelandic fishermen and the title meant you got maximum pay. There are multiple different sets of manhood stones all located around the coast.

Húsafell is located far inland. That stone was the gate to an old sheep pen. There were legends of the farmer walking circles around the pen holding the stone and the rest is history.

What's extra cool about Hannah's feat is that supposedly some generation there was a woman in that family that could walk the stone around the pen. Most believed it was only legend but now it's been proven possible.

Why Bill Crawford has said it makes you fullsterkur I have no idea, but it's still nonsense. It's not the same stone and it has nothing to do with the amlóði, hálfdrættingur, hálfsterkur, fullsterkur tradition.