It isn't actually, for a dollop of reasons. It isn't about you and body perceptions or body dysmorphias onto self or projected onto others. You clearly, have insight that you would be giving 'unreliable,' testimony, if an accurate and logical based description is of dire need, to possibly save lives.
Imo, it is silly.
As silly, as a 5ft individual, describing a forest of Birch trees, as if it were a forest of Redwood trees, when describing the place they witnessed a possible child abduction while traveling. Extremely altered perceptions of reality, because of stature, personal bias and unwilling to use logic instead of personal opionions, or body dysmorphia's all make unreliable witness testimony.
A 6'7 individual I would hope has the common sense to not describe a person they witnessed stabbing a victim as a short little petite guy who is actually 6'2 in height, weighing 320lbs, because he is a giant, and well to be expected as is in the case of short stature.
It may be silly. However, I see many on this thread differ on his appearance. As I posted earlier, my doctor considers me obese @ 5' 9 1/2" & 208 #. So @ 220# & 5' 11" probably less now I would consider him at least heavyset.