MC pads the bit-depth to report the maximum that your DAC supports with zeros on-the-fly. It plays a 16-bit file, but while it's outputting it to the DAC it reports it as 32-bit (which is useful for things like using DSP and avoid issues with some DACs with bit-depth switching) so even though it says it's 32-bit but it's still actually 16-bit. It's only a cosmetic change with reporting what's being outputted to the DAC, so it's not doing any dithering or anything like that or making any actual changes to the audio.
And no, there isn't any way to disable that and this is considered normal.
