How did I get tinnitus as a pianist?

Unknown. The auditory input such as music is processed by 2 perceptual mechanisms a) the one for individual sound and b) the perception of the pattern formed by the sound. Continuous bombardment may disrupt this hierarchical processing which in turn generates spontanous formation of sounds such as tinnitus. Or there may be an end-organ reverberation with echoes and noises of different frequencies.