I just noticed this and it made me think of something. In reality the NFL should start measuring guys from the base of the neck to the ground. 6-5 with a long neck is taller than a guy who is 6-4 with a shorter neck, but from a playing perspective they play with the same leverage and functionality. When you said he "looks shorter" that is what I thought of. I am not suggesting that is the case here, but it made me realize that not all 6-5s are equal.
Edit: Talking strictly for OL. I guess a QB needs to see over guys and maybe a WR is helped by a higher eye level. It could be different for different positions.