Yes, most likely 1 bit 'DS'.
When Sony came out with their first 1 bit DAC's they did not even mention this.
The datasheet of that player simply mentioned ... 18 bits resolution or something like that.
It was in the time that the bitrace began ... 18 bits... 20 bits etc and guess Sony did not know how to 'defend' going to 1 bit.
Technics, at the same time, came out with MASH converters and made a big deal of those.
Lots of 'technical info' on how it worked was available (I got a 2 day course in this technology when I worked for Technics)
These already were 4 bit 'ladder' DAC's that used these 4 bits in 'DS' for the smaller bits.
Talking about >20 years ago already.