Scriptural foundation:
(1 John 4:1) . . .Beloved ones, do not believe every inspired expression, but test the inspired expressions to see whether they originate with God, because many false prophets have gone forth into the world.
(Deuteronomy 18:22) 22 when the prophet speaks in the name of Jehovah and the word does not occur or come true, that is the word that Jehovah did not speak. With presumptuousness the prophet spoke it. You must not get frightened at him.. . .
*** w799/1pp.29-30pars.28-29TheRoyal"Shepherd"ofBibleProphecy ***
Unlike the clergy class, those of the Jeremiah class have been sent by Jehovah to speak in his name. .... the Jeremiah class back up their message by quoting the words, "This is what Jehovah has said." ***g933/22p.4WhySoManyFalseAlarms?***Jehovah’s Witnesses, in their eagerness for Jesus’ second coming, have suggested dates that turned out to be incorrect. Because of this, some have called them false prophets. Never in these instances, however, did they presume to originate predictions ‘in the name of Jehovah.’ Never did they say, ‘These are the words of Jehovah.’—February 15, 1981, page 19.
presumptuous - full of, characterized by, or showing presumption or readiness to presume in conduct or thought. Moses refers to presumptuousness, not lying. While liars would certainly be recognized as subject to this judgment, Moses did not say "lies" or "falsehood", he said "presumptuousness". A readiness to believe. And less than 2 years after they claimed to speak in Gods name they denied ever having said it.