I don't think that something being on the Podcast, or there being an LP of something, automatically means spoilers no longer apply.
Really now, I would understand if it's a big "twist" kind of thing, I wouldn't want to spoil something like "Who the killer is"
I have no real obligation at this point not to casually talk about THAT instance, but I wouldn't because that's a pretty big deal and it's simple courtesy not to do that.
But you know what isn't a big deal? The final boss of a game that was never presented as a "secret" in the first place, it's not some big twist thing, so getting upset about it is just making a mountain out of a mole hill.
In the context of "I've been playing it recently and I had no idea but you just spoiled that"
I would apologize because that's poor timing, I don't NEED to apologize but I would because that would suck.
In the context of "I would maybe like to play this game someday but I am not and might not in the near future."
Well you just have to get over it.