There could be lots of other factors on why this deer is small other than when it was born. I seriously doubt a doe was bred in april.... Did it get the nutrients it needed at the time it needed? Did it's mother get killed before it was fully weined? Bad genetics?
Litters of pigs always have at least one or more that is tiny. The same litter contains piglets that are twice the size of others, so that they look like they aren't from the same litter.
That deer made it through the winter, ... It survived, it's just a runt. Probably catch up this year and you'll never know.