Let us first see what a springboard means :
spring·board /ˈspriNGˌbôrd/ (Noun) :A strong, flexible board from which someone can jump in order to gain added impetus. OR A thing that lends impetus or assistance to.
Now in this sentence Spring boarded is used to tell us that his career took off like jumping off a spring board. This means that after his first few fights, he launched off to become one of the top fighters in the world.