My MIL is in LTC because she refused to get out of bed and now she has no muscle tone to be able to do it. She also has short-term memory impairment and mild/moderate dementia. Every care conference she asks when can she leave. We always tell her the doctor says she needs to be completely mobile and get out of bed and complete her ADLs on her own. She insists she's able to do this. We always tell her, "The doctor needs to do the final assessment to confirm your abilities and he'll let you know." Then she forgets she ever asked this question. She feels hopeful in the moment, we don't look like monsters to her, the staff doesn't have to suffer any fall-out of her ire and everyone leaves a calm and productive meeting. It is totally moral and ethical to tell your LO a therapeutic fib when trying to get them to remember "truth" would be more harmful.
I would only add not to feel any guilt whatsoever about where he is.
You have chosen the best care for him. Be comforted by knowing this.