According to ABRSM themselves, shape is 'effectiveness and clarity of musical shaping and detail'. And tone is 'control and projection of the sound, sensitivity and awareness in use of tonal qualities'.
So, put more simply, shape has to do with the phrasing used whilst playing, and tone to do with the dynamics.
Any piece can be phrased in different ways, rather like words in a sentence can be delivered differently, sometimes making the opposite sense from that which the writer wanted. So, playing the phrases in the style of the writer, or more musically, will give more marks,surely.
True, a piano has strings and hammers, but regardless, will be capable of being played in many different ways, and that's before pedalling gets involved. Dynamics include legato/staccato and volume changes from ppp to fff with all stops in between, let alone crescendo and diminuendo. Lots to think about!