I've run into a lot of people over the years who conflate "mistaken" with "lying." Notably, my own father. He would often say things like "Oh by the way I just got back from the store, and turns out I lied about them not being out of stock, they are." That's not lying, it's just incorrect. You THOUGHT they were in stock, and had no way of knowing without going to the store. It has to be a deliberate, knowing falsehood to be a lie. If you believe what you are saying, it isn't lying.
And this conversation has gone:
"I assert X"
"No, you're lying."
"Here's some supporting evidence to show X."
"Now you've lied twice."