It does sound right, no sense in putting him through the stress of acclimation into your stepson's tank. Keep an eye on him. If possible, don't leave him for the hermits if he dies.
Sorry about Mr. starfish. I guess we should ask, what are your current water parameters? How long has he been in your tank? It might be random, or his stomach could be a symptom of a rapid parameter shift in your tank.
Now with 30% fewer voices in my head!