So the main length of the can is the same - it's just the protruding inner pipe length is shorter on yours??

I reckon the previous owner of your bike drilled out the rivets to take off the black cone ends, then hacksawed off the inner pipe, then replaced the cones. Not sure why - maybe he wanted the holes at the end of his pipes to look bigger and tougher and the dinky one inch pipes poking out made him feel like a small man riding a postie bike...

Cosmetic reasons, I reckon, because I can't think how it would cause noticeable performance gains. Obviously a fail by the sound of it!