Meanwhile, this guy is also 5'11 and looks pretty short.
Seems to me like neck, chest length and torso width are the holy grail in not having that boxy manlet look.
I can understand where you're coming from, thinking he might appear short and I think it's because his melon is kind of big. Especially in a photo where there's nobody else to make comparisons/references to, a big head might give the illusion that he is shorter.
As with not wanting a boxy look, being skinny/thin isn't the only way to go. Look into golden age bodybuilders. Again, especially when you don't have another person to compare to right to you, you can appear taller based on your proportions and a lot of the golden age bodybuilders I would say were good at giving that illusion, small traps, big delts, wide lats, small waist and decent legs, exaggerates and makes everything appear bigger as you look upwards.
SIDE NOTE
Every UFC champion currently bar Robert Whitaker (middleweight, 185lbs) is under 6' tall and he himself is 6'0 flat at best.