I don't think the tv watching was your concern.sounds like your sis limits that, I got that it is HOW he watches it? The walking on tippy toes al the time is worth looking into too. Does your sis bring it up? Would she be willing to have him evaluated? It's touchy to suggest someone's child needs evaluating, especially a family member, hopefully you can find a way without her getting defensive. I would take him to a trusted pediatrician not a psychiatrist first, if a psychiatrist is needed the pediatrician can refer you to one. I'd want to rule out anything organic and I would imagine the ped. might want him evaluated by a pediatric neurologist. Find the best you can, that is always the key to a good diagnosis.
Usually when your gut is telling you something is wrong, it is.
Then again, what you describe could be normal too, I am sure you would have to observe it to even begin to analyse it.
What a sweet Auntie he has, good luck with getting some answers.
I'm suprised his teachers haven't brought it up, is he in school?
My doctor once told me a child should not watch more then 1 hour of tv if any. You have all reason to be worried.
It sounds more like an autistic spectrum disorder. If he is a good talker, it is more likely Asperger's Syndrome. This is generally like high functioning Autism, with relatively good speech patterns. Does he get agitated more easily than other boys his age? Is he hard to calm down if he gets upset or agitated? Whatever it is, as far as diagnosis, you do have a reasonable reason to be concerned. Try to encourage your sis to have him evaluated by a good child psychiatrist. Many of these types of problems can be managed through behavoir modification, and occupational therapy. It is not usually necessary to give a child medication unless nothing else is helping.