The phrase "false witness" refers to someone who gives dishonest or untrue information while testifying or giving evidence about an event or situation. It basically means lying or providing wrong information on purpose. Full definition
This, on a deeper level, is nothing less than the bearing of false witness. (religion-online.org)
In so far as they continue to use that name they will be false witnesses who have betrayed their trust and are misleading the people. (religion-online.org)