Hmm, that's a bit harsh, in my view. I think the mind is a very complex thing. It can play tricks on you, and it can distort the truth. So, it wouldn't be a case of them simply "not telling the truth." To the person in question, they would think that they themselves were telling the truth. Optical illusions and even hallucinations sound fair to me, but then I think it depends on each individual. The thing that you have to remember is that when you see something, your mind records that information. The moment passes and all you have is the memory. Over time, that memory could change, even just subtley. You could subconsciously add in details that weren't there before. You forget bits. You remember others. Plus, you doubt yourself. You look back and think "Was it really like that, or was it like this?"
My Mum has told me stories about her Dad, when he went to war. He said he saw a ghost, and he told the story to her in such detail. What did he see? He thinks he saw something, but we weren't their, so I guess we just have to take his word for it. A leap of faith, if you will.
That's what I find so compelling about the Barney and Betty Hill case. Its an eyewitness account, with no photographic evidence or video footage. You just have their words, their medical reports and the thoughts of critics. In my heart, I believe they saw something that wasn't from this world. Maybe that's because I want to believe, I want it to be true.