I understand that, but he's talking about a 26,000 year old fossil...<quoted text>
You honestly know next to nothing about this stuff, hey?
It's easy: you look at the bone density, muscle attachment sites and joint sizes.
Strong muscles compress bones, increasing the density (you see this not only in the mass of the bone, but in the cellular structure). Muscle attachment sites are either large (powerful muscles) or small (weak). Joints are mechanical in nature; there are mathematical relationships between the size of the parts and how much force they can take.
The above is how we know that neanderthals were so strong, they could crush the bones of your hand with a handshake. They were stronger than contemporaneous humans - but the woman my friend dug up was a human.
It's all assumptions, not fact.