Why does an image seem smaller or larger through a pinhole when viewing with human eye
I suspect this is related to distance perception and size constancy. The retinal size of an object (the actual projection of the object on your retina) decreases with 1/distance. However your visual system is compensating for this effect, which is called size constancy. For example if you put one thumb at arm length (~60cm) in front of you and another at half that distance, they will appear roughly the same size, the farther one a little smaller, while it is actually half the size of the closer one. Similarly when you look at yourself in a mirror, your face seems regular size. Next time your are in front of a mirror with condensation, draw the contour of your face in the condensation. You'll be surprised by how small it actually is. Your visual system uses distance cues to perceptually "rescale" objects so that they appear closer to their real size, and not just the size they have on the retina. This is the basis of illusions such as the corridor illusion or Ames' room.


https://en.wikipedia.org/wiki/Ames_room

To go back to your question, when looking at the keyboard through the wrapper you basically eliminate all distance cues (binocular vision, perspective...). Now in an uncontrolled experiment using uncontrolled stimuli it is a bit hard to predict what will happen perceptually, but you can assume that you'll reduce the amount of perceptual constancy and objects will appear smaller (closer to their retinal size), which seems in agreement with your observations. Why does one of your friend perceive it as larger? A similar phenomenon occurs with prisms. With prisms you artificially increase or decrease vergence angle, a cue for distance perception, while preserving the retinal size of an object. Consequently objects appear larger when you decrease vergence (because an object that would elicit the same retinal size but is farther would actually be bigger), or smaller when increase it. However is small subset of the population report perceiving the opposite effect, and as far as I know no one has provided a good explanation of why.

Picture from: Gibson, J. J. (1966). The senses considered as perceptual systems. pp 315.