Unfortunately perhaps one who...
a) is confused by runway lights that shouldn't be on
b) is tired
c) is distracted by something of which we couldn't even speculate
d) is confused by directional signs that may have been placed wrongly after recent construction/repaving
e) is drunk
f) is ....
g) is ...
h) is ...

Who knows? There could be lots of explanations -- all of them unfortunate. The only thing we can say with certainty is the poor soul paid with his life and the FO seems not to be out of danger of the same price.