He did it back when Fedor was still basically the undisputed best. Fedor was coming off of a loss to Fabricio, but even that still felt like a fluke. Fabricio had craftily caught him in a triangle to armbar transition and y'know, we still didn't want to deviate from the invincibility of Fedor.
Watching Bigfoot dominate Fedor positionally was hard(er) to watch.
You might have a revisionist take on that now, but if you're honest, or jump in a time machine and go back, Fedor was considered the best at that time, being in the UFC or not, he was the consensus greatest if not #2 at that point in time.