What are the chances that my cousin is not my uncle's child?

I was just browsing my facebook feed, when I noticed that my cousin who I have not seen in some time has uploaded a new photo of himself, and a thought crossed my mind. I found myself wondering if he is actually my uncles biological child, or if my auntie had a bit of a fling some time in the past.

See, in the photo that my cousin uploaded, you can see that he is losing his hair, as he now has a receding hairline that is very obvious. As far as I know, baldness is hereditary, and all the men in my family have a full head of hair, from myself to my brother all the way back to parents, grandparents, great grandparents and great great grandparents.

On top of this, my cousin is about 5ft 10in tall. For a man in our family, this is actually quite short. Since my great great grandfather, who was some 7ft odd inches, all men in my family have been around the 6ft 6in mark give or take.

Lastly, he does not really look like anyone else in the family. All the men have a similar shaped nose, and similar looking eyes. While my cousin has a much thinner nose, and very different eyes.

So I was wondering, based on this information. Is it likely that my auntie cheated, and that my cousin is not actually my uncles biological child?

Not that it would change anything or that I would ever say anything about it, I am just curious.