Rodney only needed that line to show how much he had understood Khan's situation. Despite their enmity, Rodney knew Khan's character quite well, and the information he had gathered in the recent period had been enough to complete that puzzle.
Things were exactly as Rodney had described them to be. Khan needed help getting a proper job on Merth 290 to avoid remaining stuck in that lawless zone and keep moving. Three species were looking for him, and staying still was bound to make them catch up.
Also, Rodney's awareness of Khan's situation confirmed what the latter had already guessed. As much as the three species had tried to contain the news, some parties had already learned about it, and they were bound to leak it even further.
Khan needed to disappear, and he had to do it quickly. Rodney had also vaguely boasted to know how to help him. He only needed something in exchange.
"What's your current rank?" Khan asked.