Was there foreshadowing? (spoilers - duh)

While the daughter and wife were still alive I was trying to figure out how is a zombie movie you could have some people fall victim while others are unaffected.

Then I thought, "what if it was blood type"? I thought it was a great idea and started writing my own script in my mind. (I was going to use AB-).

Then towards the end on the flick I find that this movie had the same idea I did. So now I wonder if there was a subtle hint at the begin of the film or am I a movie psychic?