If you look at stats of starting NFL QB height, you'll see that heights above 6'3" are the norm, with a surprising number at 6'5" and 6'6"

Labeling Wilson as small stems from a handful of things, in my opinion, including:

• Youthful Appearance. Wilson looks like he just walked out of the DMV with his learner's permit
• Slender Build. Wilson doesn't have a lot of bulk or definition in his shoulders/arms. Combine that with a flak jacket (which makes his torso appear disproportionately large and his arms disproportionately small), and you have the impression of a somewhat soft, small guy
• Taller-than-usual Offensive Line. This year's OL was unusually tall (quite a few guys were over 6'5") and that makes Wilson look smaller by comparision. This is a genuine concern, because BYU's average 2020 OL height (though not weight) was comparable to many NFL teams - so if he looked small at BYU, he's probably going to look small in the NFL, too

That said, if Wilson fails in the NFL I doubt that it will be because of height. My concerns about Wilson center on his tendency to play hero-ball, his difficulty handling pressure, and his difficulty making accurate pre- and post-snap reads against complex defensive schemes. In my opinion, even though he's on the low end, he's tall enough - and he's mobile enough that he can reset the pocket in order to open additional passing lanes/sight lines, if necessary.