If you don't believe what someone is saying, then you are saying they are lying. Why mince words? Why should I make nicey-nice about it? Let's break it down into possible options for believe Jesus' statements.
1. You believe Him.
2. You don't believe Him, but think that He is simply misinformed.
3. You don't believe Him, but think that He is lying.
I'd like to hear you try and justify either 2 or 3.
Just stop. It could also be that they understand it differently. Whether their interpretation is right or wrong accusing them of calling Jesus a liar is a false witness.