It's a calculated risk to go on the internet during or after something has aired. There is always the chance that you will accidentally see something - someone could have liked something on Facebook, it could have made the news, it could be being discussed on here, it could be anything.
It was perhaps a bad idea to put it in the thread title and not the Walking Dead thread, but the OP did apologise.
Let's not forget that it has now aired 3 times in the UK, 5 times in the US, and twice in Europe. It is widely available online, it can be paid for on Sky, it is available, if you want to watch it.
So if it was ruined for you, it's a shame, and the OP didn't mean too. It's worse when someone does purposefully post a big spoiler, and that happens ALL THE TIME on the internet. Some people are arses. But you took the risk of not watching it live, for whatever reason, and going on the internet before you'd watched it.
I have a lot of American friends, I work online, I have to be exceedingly careful on Mondays to ensure that I don't see anything that would ruin it before it airs for us. If I end up having to deal with something overnight, and it's live, I have to avoid hashtags and conversations because people talk about things as it happens.
The internet is a bit like a giant party when programs like that are on, and people talk and theorise and comfort each other. You can leave the party, or you can accept that you'll stand at the side and maybe hear something that you'd rather not have done. You can't stand in the middle and bellow that nobody can talk about it because you haven't watched it yet. It's the internet, it doesn't care. There will always be someone who is talking about it.