It's body type, I can do 70 push ups in a minute with no problem, pretty decent runner etc., but I couldn't do a proper pull-up until last year (after 3 years of rock climbing) and I still max out at 3. People making a big deal of this have no idea what they are talking about.
That said, I'm not sold on Mittlestadt and I wouldn't take him at 5, but not because of the combine.