Functional bikes. Not Porn not Anti

I think it’s a U brake on the back.

Lot of bikes that age seemed to, my old gt did too

...I never understood the rationale of having two types of brakes on one bike.

The first canti's tended to be quite wide so think a U brake on the rear was to avoid your heels applying the brakes for you.

Also have heard that people do it to get the best of both worlds as it were, or maybe to avoid having to make too many compromises, ie running a v up front provides a lot more stopping power but the pads sit closer to the rim so it's less tolerant of buckles, mud etc so run a canti on the back so that you don't have to compromise on clearance on both wheels. Or, a v on the front for the power, a canti on the rear for modulation.

I guess upgrading/replacing parts could be another reason, when a new brake standard comes out its maybe easier to change a fork than a frame so you get a mullet set up (this is pretty much why I run mullet with front disc and rear canti on my 1x1). Or you have no interest in upgrading but you damage a fork and its easier to find a v/canti fork than a ubrake one or a disc one over a rim brake one because things have moved on