My take on why Ledgic was aware of Saiyans...

So in my theory, Ledgic was an operations officer in Frieza's Army back at the time the Saiyan race was annexed (Age 730), he was in charge of a few Saiyans (the one on the left - kyuri - Japanese for "cucumber" - was Goku's grandpa, that's how he recognized him after all these years in Dragon Ball GT) whom he used to conquer planets and was aware of the Saiyans' fighting abilities & desire for bloody adventures, till they were eliminated by Frieza himself alongside their "home planet" a few years later (Age 737).

After Frieza was defeated (alongside all of his men, elites & Ginyu Force) on Planet Namek in December 24th of Age 762, Ledgic who spent most of his life under the tyrant's control decided to make a quick run for it towards freedom, yet because of the fact his homeworld was wiped by Frieza and most of his race remnants was still loyal to King Cold's family throne, he had no other option but to wander the 7th Universe and to use the only thing he had - his lifelong fighting skills - to make a living. Ledgic went on to live a life of a freelance bountyhunter and bodyguard till he was famous enough in our galaxy to be spotted/noted by the dictator Don Kee who hired him to be his main man on Planet Imecka where he gained the upper hand over the locals.