It's a nice, feel good story, oft repeated on the internet, but the evidence is dubious.

"Anthropologists" would more accurately refer specifically to Margaret Mead, a well known anthropologist. But even then, evidence of her saying it is only secondhand. When later asked in an interview, she gave a very different answer, listing things like elaborate division of labour, record keeping, and such.

But also, animals have been spotted giving basic medical care to each other in the wild. However, I could not find anything that specifically shows animals giving medical care at their own detriment to an individual who would be doomed without it.

And my own two cents: Quadrupeds can survive with a missing limb. Perhaps not as well as an unscathed individual, but still, the focus on the femur is human centric for this reason. So if anything, I think the story should ask, "How do we know when human society started?"