dabac

Hi guys,
I came across a Bridgestone City Limit, equipped with a 6-speed Hyperglide cassette.
Yes, 6-speed. Yes, Hyperglide, not Uni-glide. Splined lockring. No smallest threaded cog.
This is rare enough in it's own right, but looking at the shifter is where it gets real odd - the shifter has six clicks.
So what's up with that?
In a stock set-up, number of clicks in the shifter would be one less than the number of sprockets.
And if this is a 7-speed shifter, how come it's indexing nicely on the 6-speed cassette?
Does it use a shorter body than the 7-speed, just like 7- speed uses a shorter body than 8/9/10-speed?

Any experience would be appreciated.