I think it's only for dishnetwork and directv subscribers. I had cable before and usually they only give NBATV free for a week when LP is free for DISH and DIRECTV.
We actually had dish and cable before. But now we have directv. All I know is, I never got free LP with cable so we switched.
I'm not sure about Comcast so someone else should be able to help.
You could try calling your cable provider and ask about it. It (Free week) ends tomorrow, btw.