OMG I have a NHR that looks just like that at 4 weeks and we had the same question Looks like we got a roo in our mix as well. So much for the hatchery sending all females.
I just received a new order from McMurray (Apr 2015) and have four more just like this in the bunch. I would have laid down my last dollar on rooster....but got a nice surprise when I waited because I wanted hens. I will wait these new four out as well.