An of course the Zeiss Ikon meter is center-weighted, not spot, so the light reflected from beside the trousers also comes to play.
In general spot metering is the only consistent way to get a backlighted object correctly exposed without resorting to a hand-held meter. With center-weighted or multi-segment (a.k.a. evaluative or matrix) metering only experience will tell you how the meter actually works in such situations. Once you learn that, you can usually apply the desired compensation. Multi-segment metering systems typically apply automatic backlight compensation, but it may not be sufficient or it may be overdone.
All this is of course less of a problem with digital, since you can always check the results. This is merely a statement of fact and not an endorsement of digital imaging. I am a 95% film photographer myself.
A good basic explanation about different light metering systems and their use:
http://www.great-landscape-photography.com/metering.html