To respond to the replies to my post I do not know exactly what I saw, though it was a Hohner, had what looked like about a 2.5 octave piano keyboard (it was slightly larger than my Pockerwork melodeon) and the bass buttons were about the same size as melodeon bass buttons and arranged in two parallel rows like a melodeon. From the design, I would guess it was quite an old instrument.

Unfortunately, I did not get a chance to ask the owner about it.