ALL rod pairs on vee type engines have a slight amount of front to rear clearance, you just didn't find it in the other pairs. The number can get pretty loose there. Need at least the minimum  number the engine specs specify, too tight and the oil flow is trapped and you can then burn up a rod bearing. The side clearance serves as an oil metering device just like the actual clearance to the journal itself. Why both get loosened up a bit on race engines. With all mismatched pieces when rebuilding you swap out rods to somewhat even out that clearance between all pairs, it does not have to be exact.