I believe that says more about his willingness and attitude than fitness (which obviously also is great). But really, it's desire and determination that sees a player run 12 km in one match. The physical side of things isn't that impressive. Any super-pro footballer CAN run 12 kilometres in one match, but those who stand out are those who have enough of a desire to actually put in a decent day's work.
The head coach of Denmarks national team, Åge Hareide, is visiting the Norwegian Champions League studio tonight. He was asked what he thinks of Eriksen's future, if he dreams of going to Barcelona.
He replied that Eriksen is a down to earth guy, for him being happy is more important than high wages and being a celebrity. Furthermore, he thought that Eriksen is very happy at Spurs, working with Poch, Dele and Kane, and didn't see any reason he should leave Tottenham.
Doesn't mean anything necessarily, but it's good to hear.