Answer:
There are two possible explanations for this (or three if you believe in spontaneous generation).
#1
They were extinct in the wild but still alive in captivity and then reintroduced into the wild.
#2
They were in the wild but no one came across them, that's to say they were very endangered, and thus there were so few that none were seen
#3
They spontainiosly came into existence, this is known as "spontaneos generation" and was a thing a long time ago