Let's take a simple case where most people would want to avoid being relativists. Let's take the claim that the world is round. If someone thought the earth was flat, and then went around the world on a ship, it looks as if the sensible conclusion would be that they were in error about that, that the thought the earth was flat, but it turns out to be round.
Now, let's try something else. We may be unsure as to who committed the Jack the Ripper murders, since the case was never solved. But we do know that someone did. That seems to suggest to me that even in cases where we don't have sufficient evidence that something is true, sufficient to convince a jury beyond reasonable doubt, we still believe that someone is right about it. Thus, many people believe that O. J. Simpson killed Nicole Brown Simpson and Ronald Goldman, even though the jury didn't think there was enough evidence for a conviction.
Of course, being right doesn't mean being justified in one's belief. Thus, I can get the right answer to a math problem by guessing. It's still the right answer, even if the teacher doesn't give me credit for it because I didn't show my work.
Now let's consider a scenario in the matter of religious belief. Suppose a person were to be an atheist throughout their lives, and a person who does not believe in life after death (as almost all atheists do). Suppose this atheist were to die, but continue to exist, and were then to experience the presence of a very powerful being on a white throne (let's say), and that being on the throne were to ask the atheist why he did not believe in his existence during his lifetime. (We can imagine this atheist being sent to overheated living quarters thereafter). Wouldn't the sensible think for this atheist to say be that those darned Christians were right after all?