If it knew to flee when you were billions of kms away, perhaps it's a Prix take on an AWACS ship? Either that, or there's another Prix ship with sensors near the jump point, or the Prix are cheaters. If it is an AWACS ship, that would explain it keeping its distance.
Well... that captured Prix 250,000,000 range active sensor must be detectable an awful long way away, to any race at their tech level.
Our first two Rock-III decoy vessels have been completed. Twenty layers of armor and 5625 kps speed.