strange keyboard on a 18th century painting

on this link

http://rmc.library.cornell.edu/mozart/images_imagined/Count_Firmian.htm

There is a misattributed portrait of Mozart with a very peculiar
keyboard. Is it just en error from the painter or such thing have
historical existence?

with keys arragement changing from octave to octave, I would guess
for an error. any ideas?

François Laferrière

I think there is a tradition of art works being a bit "unrealistic" in its
representations of musical subjects. There are lots of paintings that show
impossibilities and other liberties when using a music subject. I remember
learning about this while taking a course with Leeman Perkins at Columbia.
It may be the result of meshing realism with a poetic license.

best, Johnny Reinhard