Can someone explain the season pass for “Batman: The Enemy Within” to me?

According to the listing on the PlayStation Store, the Season Pass includes all 5 episodes. Other Telltale games have similar lines in their Season Passes too. If it needed it, there's be a line that said something like "This requires Episode 1 to be playable", like if you look at just Episode 2.

I think the way they did it for the disc releases was, episode 1 is on the disc already and the other episodes you have to download as an update. Because they released the disc before the other episodes were available for some of the telltale seasons.

Those Telltale Games titles were released in such a way that although they came out in seasons, just owning the game got you every season. They didn't have paid expansions. I'd double check and make sure the, "Season pass" isn't really just the whole game. They usually have 5 seasons total.

Oh, and don't get too spooked when you see you still have to download each season individually. They'll still be free. It's just the way those titles are.