If I said I sat on the couch and ate some potato chips, you would probably just take my word for it. If I said aliens abducted me and took me to mars where we had a party, you would probably want strong evidence. You are not going to take my word for it. Even if there was 5 eye witnesses you would probably still wouldn't believe it. The more crazy situation needs more evidence because it is so out there.

I think you are taking the phrase a little too literal. It isn't about having extraordinary evidence, but just having solid evidence for the claim you make. The bigger the claim the more evidence you need. Like in my example, having the empty bag of potato chips would probably be sufficient for the first, however for the second you need evidence to support aliens exist, that people can survive on mars, and that they abducted you.

In the case of the afterlife, if you are making claims that you know exactly what happens when you die, you need proof that there is an afterlife, and that it is the way you described.