Somehow, I think Chomper is the actual target. Ruby has gone out into the Mysterious Beyond to find her family during “Return to Hanging Rock”, yet Chomper, at least that we know of, has not gone into the Mysterious Beyond to try and contact his own parents.
This would almost seem to imply 1 of 2 things (and maybe, both):
1.) Chomper is actually the one Red Claw is after. For some reason, he got Ruby to help him and help him when he had to leave his parents. Also, Red Claw must have more at his side than just Screech and Thud. Perhaps his parents were afraid of being attacked too or afraid that Red Claw would attack in the night.
2.) Chomper’s parents are dead (either they couldn’t get off the Mysterious Island and died of hunger or else they were killed by Red Claw). Hence, there is nobody to visit.
Now, my own theory is that one day, Ruby was cornered by Red Claw and Chomper had rescued her, perhaps hurting Red Claw in the process. Red Claw is furious at Chomper for hurting him and causing him to lose his meal. Ruby, feeling she owes Chomper for saving him, has agreed to help take care of him.