The visual typing thing is socionics, I think. I am using muscle tension, which can be similar but is a little different.
I don’t think that every person in a type ends up with the same kind of body, or silhouette, although occasionally similarities do crop up (and certainly some INTPs look as you’ve described). I do think that if you have two people from the same type performing the same activity, they are likely to use their muscles in the same way to accomplish that activity.
In this way, I think expressions and movements tend to be more similar across type than physical features.