The Posuk says (Genesis 42:8):
וַיַּכֵּר יוֹסֵף אֶת אֶחָיו וְהֵם לֹא הִכִּרֻהוּ
Now Joseph recognized his brothers, but they did not recognize him
The question is: How did they miss all the signs that were there:
- In Posuk 42:18 he says "אֶת הָאֱ־לֹהִים אֲנִי יָרֵא", "I fear GOD".
- And if you take the Gemara in Chulin 91a on a pshat level, he Shechted (ritually slaughtered) the animal and removed the Gid Hanashe (did Nikur). After seeing this, how did they not recognize him as Yosef their brother?