HTM,
It's possible that a race spring may not have the fatigue life that a street spring does. Not saying that's necessarily the case with this particular one; it is a possibility.
Race springs are generally expendable - when you refresh the engine after what would be a very low number of miles compared with street use, the valve springs would normally be replaced. The racing miles would indeed be quite harsh, but not near as many cycles as, say, a few thousand miles on the street.
I usually specify "dump truck" parts for my engines to avoid shorter life cycle parts as used in racing.
Just sayin',
Tom