Damn, I've been doing things wrong this entire time them. The only cub I've encountered in my 5-6 playthroughs was the one in the cave whose mother killed that True Soul. I had no idea there was an owlbear in the goblin camp.
It's the same owlbear cub. If you kill the mother and leave him alive, he ends up getting caught by the goblins. They take him back to their camp and use him for their "chicken chase" game. You have to win the chicken chase game, and either win some animal handling roles or use speak with animals to get him to know you're on his side. Then when you start killing the goblins, he will run off.
I never did it this way, but I heard you can also denounce chicken chasing as a cruel sport and insist you're taking the cub. Then you'll have to either intimidate or use the illithid power against the goblin female running the game. After winning that you hope the cub will be able to follow your scent to your camp. I just looked it up and saw that the option to denounce chicken chasing only shows up if you go back to the goblin and ask her to explain the rules a second time. That's probably why I never saw that option.
Either way after you kill the goblins in the courtyard, the cub will show up at your camp 2 or 3 nights later. Feed it and it will run off, but then it will come back and hang around.
Also, you don't have to poison their drinks to kill all the goblins in the courtyard, but it does help to cut down their numbers. As well as leave survivors with lower hit points so they are easier to kill. You can also kill the goblins in the center courtyard without triggering the ones on the side, as long as none of your characters runs over to that side. Keep your characters on the side with the chicken chasing course.