You read that in native hawaiians, the probability of having blood type ab is 1/100 (1 in 100). this means that

This means that if you pick 100 Hawaians randomly, the fraction of them having blood type AB will be close to 1/100. Probability is a statistical term describing the likelihood that an event will occur, in this case, the likelihood of a native Hawaian having an AB blood type. 1 in 100 means that out of 100 people randomly chosen the amount of them having this blood type will be very close to 1. Since the sample population is randomly chosen, it can not be certain that only 1 out of 100 will have this blood type.