This comic is it's own universe, not really connected to anything else. But, I do think it expects you to be familiar with Thundercats as a concept. Because, it's not really exploring or elaborating on a lot of these ideas in this first issue. It summarizes things, but it's not really building up the world or anything right now.
Also, yeah, I'm not sure if it did release digitally today or not? This reddit thread has a few people who can't find it either, but one person says it's released?
reddit.com/r/Thundercats/comments/1aizc89/will_it_be_released_digitally/
So, if it DID release today, they made it pretty hard to find. And it's not really a publisher thing, because I checked and all the Gargoyles comics, which Dynamite also does, are up to date and up on Amazon. So, I'm not sure what's going on.