It's stated in the Japanese version of the film by Tullece their similarity is due to them both being lower-class Saiyans. Genetics is likely the main factor in rank, at least in Toei's continuity where 10k Bardock was still a low-class, plus the Saiyans are known for having always been a race of fairly small numbers. It'd make sense if the genetic difference between some Saiyans were akin to those of distant relatives separated by a couple of generations.