Pence was simply repeating what he was told, at the time there was no reason to doubt what Flynn told him.
Now there is reason to doubt him and he was removed, trusting someone until they prove to be untrustworthy is not evil. Maybe Pence should have less trusting, maybe not, but the fact remains that at no time was Pence telling a lie, he may not have been correct but at the time he had no other information proving otherwise.
The media reported that Russians hacked into the power grid, later they had to retract that story. Did the Washington Pose tell a lie? Certainly they reported something that was blatantly false, but was it a lie to repeat something that others told you was true?
In Pence’s case the information came from someone he thought was trustworthy so he felt confident repeating it, but in the Washington post story it was just an anonymous source, not really someone trustworthy.