It sounds to me like your son is using the monthly paid service, SlingTV, which is the only "Sling"-related application that will pull up on an Xbox. The SlingTV service is not our service, and we are not affiliated with them in any way. It would not surprise me if you are receiving information about Slingboxes when contacting our support line, because that is the product/service we work with.
I pulled up a link concerning Xbox/SlingTV that you should have some better luck with:
You should be able to receive support for SlingTV by reaching out to 1-888-291-5217.
Sorry about the confusion!